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| Oracle8 Application Developer's Guide Release 8.0 A58241-01 |
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This chapter discusses the procedural capabilities of Oracle, including:
PL/SQL is a modern, block-structured programming language. It provides you with a number of features that make developing powerful database applications very convenient. For example, PL/SQL provides procedural constructs, such as loops and conditional statements, that you do not find in standard SQL.
You can directly issue SQL data manipulation language (DML) statements inside PL/SQL blocks, and you can use procedures, supplied by Oracle, to perform data definition language (DDL) statements.
PL/SQL code executes on the server, so using PL/SQL allows you to centralize significant parts of your database applications for increased maintainability and security. It also enables you to achieve a significant reduction of network overhead in client/server applications.
You can even use PL/SQL for some database applications in place of 3GL programs that use embedded SQL or the Oracle Call Interface (OCI).
There are several kinds of PL/SQL program units:
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See Also:
For complete information about the PL/SQL language, see the PL/SQL User's Guide and Reference. |
An anonymous PL/SQL block consists of an optional declarative part, an executable part, and one or more optional exception handlers.
You use the declarative part to declare PL/SQL variables, exceptions, and cursors. The executable part contains PL/SQL code and SQL statements, and can contain nested blocks. Exception handlers contain code that is called when the exception is raised, either as a predefined PL/SQL exception (such as NO_DATA_FOUND or ZERO_DIVIDE), or as an exception that you define.
The following short example of a PL/SQL anonymous block prints the names of all employees in department 20 in the EMP table, using the DBMS_OUTPUT package (described on page 12-22):
DECLARE emp_name VARCHAR2(10); CURSOR c1 IS SELECT ename FROM emp WHERE deptno = 20; BEGIN LOOP FETCH c1 INTO emp_name; EXIT WHEN c1%NOTFOUND; DBMS_OUTPUT.PUT_LINE(emp_name); END LOOP; END;
Exceptions allow you to handle Oracle error conditions within PL/SQL program logic. This allows your application to prevent the server from issuing an error that could cause the client application to abort. The following anonymous block handles the predefined Oracle exception NO_DATA_FOUND (which would result in an ORA-01403 error if not handled):
DECLARE emp_number INTEGER := 9999; emp_name VARCHAR2(10); BEGIN SELECT ename INTO emp_name FROM emp WHERE empno = emp_number; -- no such number DBMS_OUTPUT.PUT_LINE('Employee name is ' || emp_name); EXCEPTION WHEN NO_DATA_FOUND THEN DBMS_OUTPUT.PUT_LINE('No such employee: ' || emp_number); END;
You can also define your own exceptions, declare them in the declaration part of a block, and define them in the exception part of the block. An example follows:
DECLARE emp_name VARCHAR2(10); emp_number INTEGER; empno_out_of_range EXCEPTION; BEGIN emp_number := 10001; IF emp_number > 9999 OR emp_number < 1000 THEN RAISE empno_out_of_range; ELSE SELECT ename INTO emp_name FROM emp WHERE empno = emp_number; DBMS_OUTPUT.PUT_LINE('Employee name is ' || emp_name); END IF; EXCEPTION WHEN empno_out_of_range THEN DBMS_OUTPUT.PUT_LINE('Employee number ' || emp_number || ' is out of range.'); END;
Anonymous blocks are most often used either interactively, from a tool such as SQL*Plus, or in a precompiler, OCI, or SQL*Module application. They are normally used to call stored procedures, or to open cursor variables.
A database trigger is a special kind of PL/SQL anonymous block. You can define triggers to fire before or after SQL statements, either on a statement level or for each row that is affected. See Chapter 13, "Using Database Triggers" in this Guide for more information.
A stored procedure or function is a PL/SQL program unit that
Since a procedure is stored in the database, it must be named, to distinguish it from other stored procedures, and to make it possible for applications to call it. Each publicly-visible procedure in a schema must have a unique name. The name must be a legal PL/SQL identifier.
Procedure and function names that are part of packages can be overloaded. That is, you can use the same name for different subprograms as long as their formal parameters differ in number, order, or datatype family. See PL/SQL User's Guide and Reference for more information about subprogram name overloading.
Stored procedures and functions can take parameters. The following example shows a stored procedure that is similar to the anonymous block on page 10-3:
PROCEDURE get_emp_names (dept_num IN NUMBER) IS emp_name VARCHAR2(10); CURSOR c1 (depno NUMBER) IS SELECT ename FROM emp WHERE deptno = depno; BEGIN OPEN c1(dept_num); LOOP FETCH c1 INTO emp_name; EXIT WHEN c1%NOTFOUND; DBMS_OUTPUT.PUT_LINE(emp_name); END LOOP; CLOSE c1; END;
In the stored procedure example, the department number is an input parameter, which is used when the parameterized cursor C1 is opened.
The formal parameters of a procedure have three major parts:
You use parameter modes to define the behavior of formal parameters. The three parameter modes, IN (the default), OUT, and IN OUT, can be used with any subprogram. However, avoid using the OUT and IN OUT modes with functions. The purpose of a function is to take zero or more arguments and return a single value. It is poor programming practice to have a function return multiple values. Also, functions should be free from side effects, which change the values of variables not local to the subprogram.
Table 10-1 summarizes the information about parameter modes. Parameter modes are explained in detail in the PL/SQL User's Guide and Reference.
The datatype of a formal parameter consists of one of the following:
NUMBER or VARCHAR2
%TYPE or %ROWTYPE attributes
However, you can use the type attributes %TYPE and %ROWTYPE to constrain the parameter. For example, the GET_EMP_NAMES procedure specification in "Procedure Parameters" on page 10-5 could be written as
PROCEDURE get_emp_names(dept_num IN emp.deptno%TYPE)
to have the DEPT_NUM parameter take the same datatype as the DEPTNO column in the EMP table. The column and table must be available when a declaration using %TYPE (or %ROWTYPE) is elaborated.
Using %TYPE is recommended, since if the type of the column in the table changes, it is not necessary to change the application code.
If the GET_EMP_NAMES procedure is part of a package, then you can use previously-declared public (package) variables to constrain a parameter datatype. For example:
dept_number number(2); ... PROCEDURE get_emp_names(dept_num IN dept_number%TYPE);
You use the %ROWTYPE attribute to create a record that contains all the columns of the specified table. The following example defines the GET_EMP_REC procedure, which returns all the columns of the EMP table in a PL/SQL record, for the given EMPNO:
PROCEDURE get_emp_rec (emp_number IN emp.empno%TYPE, emp_ret OUT emp%ROWTYPE) IS BEGIN SELECT empno, ename, job, mgr, hiredate, sal, comm, deptno INTO emp_ret FROM emp WHERE empno = emp_number; END;
You could call this procedure from a PL/SQL block as follows:
DECLARE emp_row emp%ROWTYPE; -- declare a record matching a -- row in the EMP table BEGIN get_emp_rec(7499, emp_row); -- call for emp# 7499 DBMS_OUTPUT.PUT(emp_row.ename || ' ' || emp_row.empno); DBMS_OUTPUT.PUT(' ' || emp_row.job || ' ' || emp_row.mgr); DBMS_OUTPUT.PUT(' ' || emp_row.hiredate || ' ' || emp_row.sal); DBMS_OUTPUT.PUT(' ' || emp_row.comm || ' ' || emp_row.deptno); DBMS_OUTPUT.NEW_LINE; END;
Stored functions can also return values that are declared using %ROWTYPE. For example:
FUNCTION get_emp_rec (dept_num IN emp.deptno%TYPE) RETURN emp%ROWTYPE IS ...
You can pass PL/SQL tables as parameters to stored procedures and functions. You can also pass tables of records as parameters.
Parameters can take default values. You use the DEFAULT keyword or the assignment operator to give a parameter a default value. For example, the specification for the GET_EMP_NAMES procedure on page 10-5 could be written as
PROCEDURE get_emp_names (dept_num IN NUMBER DEFAULT 20) IS ...
or as
PROCEDURE get_emp_names (dept_num IN NUMBER := 20) IS ...
When a parameter takes a default value, it can be omitted from the actual parameter list when you call the procedure. When you do specify the parameter value on the call, it overrides the default value.
Unlike in an anonymous PL/SQL block, you do not use the keyword DECLARE before the declarations of variables, cursors, and exceptions in a stored procedure. In fact, it is an error to use it.
Use your normal text editor to write the procedure. At the beginning of the procedure, place the command
CREATE PROCEDURE procedure_name AS ...
For example, to use the example on page 10-8, you can create a text (source) file called get_emp.sql containing the following code:
CREATE PROCEDURE get_emp_rec (emp_number IN emp.empno%TYPE, emp_ret OUT emp%ROWTYPE) AS BEGIN SELECT empno, ename, job, mgr, hiredate, sal, comm, deptno INTO emp_ret FROM emp WHERE empno = emp_number; END; /
Then, using an interactive tool such as SQL*Plus, load the text file containing the procedure by entering the command
SQLPLUS> @get_emp
to load the procedure into the current schema from the get_emp.sql file (.sql is the default file extension). Note the slash (/) at the end of the code. This is not part of the code; it just activates the loading of the procedure.
You can use either the keyword IS or AS after the procedure parameter list.
Use the CREATE [OR REPLACE] FUNCTION... command to store functions. See the Oracle8 SQL Reference for the complete syntax of the CREATE PROCEDURE and CREATE FUNCTION commands.
To create a stand-alone procedure or function, or package specification or body, you must meet the following prerequisites:
CREATE PROCEDURE system privilege to create a procedure or package in your schema, or the CREATE ANY PROCEDURE system privilege to create a procedure or package in another user's schema.
If the privileges of a procedure's or package's owner change, the procedure must be reauthenticated before it is executed. If a necessary privilege to a referenced object is revoked from the owner of the procedure (or package), the procedure cannot be executed.
The EXECUTE privilege on a procedure gives a user the right to execute a procedure owned by another user. Privileged users execute the procedure under the security domain of the procedure's owner. Therefore, users never have to be granted the privileges to the objects referenced by a procedure. This allows for more disciplined and efficient security strategies with database applications and their users. Furthermore, all procedures and packages are stored in the data dictionary (in the SYSTEM tablespace). No quota controls the amount of space available to a user who creates procedures and packages.
To alter a stored procedure or stored function, you must first DROP it, using the DROP PROCEDURE or DROP FUNCTION command, then recreate it using the CREATE PROCEDURE or CREATE FUNCTION command. Alternatively, use the CREATE OR REPLACE PROCEDURE or CREATE OR REPLACE FUNCTION command, which first drops the procedure or function if it exists, then recreates it as specified.
A PL/SQL procedure executing on an Oracle Server can call an external procedure, written in a 3GL. The 3GL procedure executes in a separate address space from that of the Oracle Server.
A package is a group of PL/SQL types, objects, and stored procedures and functions. The specification part of a package declares the public types, variables, constants, and subprograms that are visible outside the immediate scope of the package. The body of a package defines the objects declared in the specification, as well as private objects that are not visible to applications outside the package.
The following example shows a package specification for a package named EMPLOYEE_MANAGEMENT. The package contains one stored function and two stored procedures.
CREATE PACKAGE employee_management AS FUNCTION hire_emp (name VARCHAR2, job VARCHAR2, mgr NUMBER, hiredate DATE, sal NUMBER, comm NUMBER, deptno NUMBER) RETURN NUMBER; PROCEDURE fire_emp (emp_id NUMBER); PROCEDURE sal_raise (emp_id NUMBER, sal_incr NUMBER); END employee_management;
The body for this package defines the function and the procedures:
CREATE PACKAGE BODY employee_management AS FUNCTION hire_emp (name VARCHAR2, job VARCHAR2, mgr NUMBER, hiredate DATE, sal NUMBER, comm NUMBER, deptno NUMBER) RETURN NUMBER IS -- The function accepts all arguments for the fields in -- the employee table except for the employee number. -- A value for this field is supplied by a sequence. -- The function returns the sequence number generated -- by the call to this function. new_empno NUMBER(10); BEGIN SELECT emp_sequence.NEXTVAL INTO new_empno FROM dual; INSERT INTO emp VALUES (new_empno, name, job, mgr, hiredate, sal, comm, deptno); RETURN (new_empno); END hire_emp; PROCEDURE fire_emp(emp_id IN NUMBER) AS -- The procedure deletes the employee with an employee -- number that corresponds to the argument EMP_ID. If -- no employee is found, an exception is raised. BEGIN DELETE FROM emp WHERE empno = emp_id; IF SQL%NOTFOUND THEN raise_application_error(-20011, 'Invalid Employee Number: ' || TO_CHAR(emp_id)); END IF; END fire_emp; PROCEDURE sal_raise (emp_id IN NUMBER, sal_incr IN NUMBER) AS -- The procedure accepts two arguments. EMP_ID is a -- number that corresponds to an employee number. -- SAL_INCR is the amount by which to increase the -- employee's salary. BEGIN -- If employee exists, update salary with increase. UPDATE emp SET sal = sal + sal_incr WHERE empno = emp_id; IF SQL%NOTFOUND THEN raise_application_error(-20011, 'Invalid Employee Number: ' || TO_CHAR(emp_id)); END IF; END sal_raise; END employee_management;
Each part of a package is created with a different command. Create the package specification using the CREATE PACKAGE command. The CREATE PACKAGE command declares public package objects.
To create a package body, use the CREATE PACKAGE BODY command. The CREATE PACKAGE BODY command defines the procedural code of the public procedures and functions declared in the package specification. (You can also define private (or local) package procedures, functions, and variables within the package body. See "Local Objects" on page 10-15.
It is often more convenient to add the OR REPLACE clause in the CREATE PACKAGE or CREATE PACKAGE BODY commands when you are first developing your application. The effect of this option is to drop the package or the package body without warning. The CREATE commands would then be
CREATE OR REPLACE PACKAGE package_name AS ...
and
CREATE OR REPLACE PACKAGE BODY package_name AS ...
The privileges required to create a package specification or package body are the same as those required to create a stand-alone procedure or function; see page 10-10.
The body of a package can contain
Procedures, functions, cursors, and variables that are declared in the package specification are global. They can be called, or used, by external users that have execute permission for the package, or that have EXECUTE ANY PROCEDURE privileges.
When you create the package body, make sure that each procedure that you define in the body has the same parameters, by name, datatype, and mode, as the declaration in the package specification. For functions in the package body, the parameters as well as the return type must agree in name and type.
You can define local variables, procedures, and functions in a package body. These objects can only be accessed by other procedures and functions in the body of the same package. They are not visible to external users, regardless of the privileges they hold.
The names of a package and all public objects in the package must be unique within a given schema. The package specification and its body must have the same name. All package constructs must have unique names within the scope of the package, unless overloading of procedure names is desired.
A stand-alone procedure, a stand-alone function, a package body, or an entire package can be dropped using the SQL commands DROP PROCEDURE, DROP FUNCTION, DROP PACKAGE BODY, and DROP PACKAGE, respectively. A DROP PACKAGE statement drops both a package's specification and body.
The following statement drops the OLD_SAL_RAISE procedure in your schema:
DROP PROCEDURE old_sal_raise;
To drop a procedure or package, the procedure or package must be in your schema or you must have the DROP ANY PROCEDURE privilege. An individual procedure within a package cannot be dropped; the containing package specification and body must be re-created without the procedures to be dropped.
Each session that references a package object has its own instance of the corresponding package, including persistent state for any public and private variables, cursors, and constants. If any of the session's instantiated packages (specification or body) are subsequently invalidated and recompiled, all other dependent package instantiations (including state) for the session are lost.
For example, assume that session S instantiates packages P1 and P2, and that a procedure in package P1 calls a procedure in package P2. If P1 is invalidated and recompiled (for example, as the result of a DDL operation), the session S instantiations of both P1 and P2 are lost. In such situations, a session receives the following error the first time it attempts to use any object of an invalidated package instantiation:
ORA-04068: existing state of packages has been discarded
The second time a session makes such a package call, the package is reinstantiated for the session without error.
In most production environments, DDL operations that can cause invalidations are usually performed during inactive working hours; therefore, this situation might not be a problem for end-user applications. However, if package specification or body invalidations are common in your system during working hours, you might want to code your applications to detect for this error when package calls are made. For example, the user-side application might reinitialize any user-side state that depends on any session's package state (that was lost) and reissue the package call.
Dependencies among PL/SQL library units (packages, stored procedures, and stored functions) can be handled in two ways:
If timestamps are used to handle dependencies among PL/SQL library units, whenever you alter a library unit or a relevant schema object all of its dependent units are marked as invalid and must be recompiled before they can be executed.
Each library unit carries a timestamp that is set by the server when the unit is created or recompiled. Figure 10-1 demonstrates this graphically. Procedures P1 and P2 call stored procedure P3. Stored procedure P3 references table T1. In this example, each of the procedures is dependent on table T1. P3 depends upon T1 directly, while P1 and P2 depend upon T1 indirectly.
If P3 is altered, P1 and P2 are marked as invalid immediately if they are on the same server as P3. The compiled states of P1 and P2 contain records of the timestamp of P3. So if the procedure P3 is altered and recompiled, the timestamp on P3 no longer matches the value that was recorded for P3 during the compilation of P1 and P2.
If P1 and P2 are on a client system, or on another Oracle Server in a distributed environment, the timestamp information is used to mark them as invalid at runtime.
The disadvantage of this dependency model is that is unnecessarily restrictive. Recompilation of dependent objects across the network are often performed when not strictly necessary, leading to performance degradation.
Furthermore, on the client side, the timestamp model can lead to situations that block an application from running at all, if the client-side application is built using PL/SQL version 2. (Earlier releases of tools such as Oracle Forms that used PL/SQL version 1 on the client side did not use this dependency model, since PL/SQL version 1 had no support for stored procedures.)
For releases of Oracle Forms that are integrated with PL/SQL version 2 on the client side, the timestamp model can present problems. First of all, during the installation of the application, the application is rendered invalid unless the client-side PL/SQL procedures that it uses are recompiled at the client site. Also, if a client-side procedure depends on a server procedure, and the server procedure is changed or automatically recompiled, the client-side PL/SQL procedure must then be recompiled. Yet in many application environments (such as Forms runtime applications), there is no PL/SQL compiler available on the client. This blocks the application from running at all. The client application developer must then redistribute new versions of the application to all customers.
To alleviate some of the problems with the timestamp-only dependency model, Oracle provides the additional capability of remote dependencies using signatures. The signature capability affects only remote dependencies. Local (same server) dependencies are not affected, as recompilation is always possible in this environment.
The signature of a subprogram contains information about the
IN, OUT, IN OUT)
The user has control over whether signatures or timestamps govern remote dependencies. See "Controlling Remote Dependencies" on page 10-24 for more information. If the signature dependency model is in effect, a dependency on a remote library unit causes an invalidation of the dependent unit if the dependent unit contains a call to a subprogram in the parent unit, and the signature of this subprogram has been changed in an incompatible manner.
For example, consider a procedure GET_EMP_NAME stored on a server BOSTON_SERVER. The procedure is defined as
CREATE OR REPLACE PROCEDURE get_emp_name ( emp_number IN NUMBER, hire_date OUT VARCHAR2, emp_name OUT VARCHAR2) AS BEGIN SELECT ename, to_char(hiredate, 'DD-MON-YY') INTO emp_name, hire_date FROM emp WHERE empno = emp_number; END;
When GET_EMP_NAME is compiled on the BOSTON_SERVER, its signature as well as its timestamp is recorded.
Now assume that on another server, in California, some PL/SQL code calls GET_EMP_NAME identifying it using a DBlink called BOSTON_SERVER, as follows:
CREATE OR REPLACE PROCEDURE print_ename ( emp_number IN NUMBER) AS hire_date VARCHAR2(12); ename VARCHAR2(10); BEGIN get_emp_name@BOSTON_SERVER( emp_number, hire_date, ename); dbms_output.put_line(ename); dbms_output.put_line(hiredate); END;
When this California server code is compiled, the following actions take place:
GET_EMP_NAME is transferred to the California server
PRINT_ENAME
At runtime, during the remote procedure call from the California server to the Boston server, the recorded signature of GET_EMP_NAME that was saved in the compiled state of PRINT_ENAME gets sent across to the Boston server., regardless of whether there were any changes or not.
If the timestamp dependency mode is in effect, a mismatch in timestamps causes an error status to be returned to the calling procedure.
However, if the signature mode is in effect, any mismatch in timestamps is ignored, and the recorded signature of GET_EMP_NAME in the compiled state of PRINT_ENAME on the California server is compared with the current signature of GET_EMP_NAME on the Boston server. If they match, the call succeeds. If they do not match, an error status is returned to the PRINT_NAME procedure.
Note that the GET_EMP_NAME procedure on the Boston server could have been changed. Or, its timestamp could be different from that recorded in the PRINT_NAME procedure on the California server, due to, for example, the installation of a new release of the server. As long as the signature remote dependency mode is in effect on the California server, a timestamp mismatch does not cause an error when GET_EMP_NAME is called.
A signature is associated with each compiled stored library unit. It identifies the unit using the following criteria:
A signature changes when you change from one class of datatype to another. Within each datatype class, there can be several types. Changing a parameter datatype from one type to another within a class does not cause the signature to change.
Table 10-2 shows the classes of types.
Changing to or from an explicit specification of the default parameter mode IN does not change the signature of a subprogram. For example, changing
PROCEDURE P1 (param1 NUMBER);
to
PROCEDURE P1 (param1 IN NUMBER);
does not change the signature. Any other change of parameter mode does change the signature.
Changing the specification of a default parameter value does not change the signature. For example, procedure P1 has the same signature in the following two examples:
PROCEDURE P1 (param1 IN NUMBER := 100); PROCEDURE P1 (param1 IN NUMBER := 200);
An application developer who requires that callers get the new default value must recompile the called procedure, but no signature-based invalidation occurs when a default parameter value assignment is changed.
In the GET_EMP_NAME procedure defined on page 10-5, if the procedure body is changed to
BEGIN -- date format model changes SELECT ename, to_char(hiredate, 'DD/MON/YYYY') INTO emp_name, hire_date FROM emp WHERE empno = emp_number; END;
then the specification of the procedure has not changed, and so its signature has not changed.
But if the procedure specification is changed to
CREATE OR REPLACE PROCEDURE get_emp_name ( emp_number IN NUMBER, hire_date OUT DATE, emp_name OUT VARCHAR2) AS
and the body is changed accordingly, then the signature changes, because the parameter HIRE_DATE has a different datatype.
However, if the name of that parameter changes to WHEN_HIRED, and the datatype remains VARCHAR2, and the mode remains OUT, then the signature does not change. Changing the name of a formal parameter does not change the signature of the unit.
Consider the following example:
CREATE OR REPLACE PACKAGE emp_package AS TYPE emp_data_type IS RECORD ( emp_number NUMBER, hire_date VARCHAR2(12), emp_name VARCHAR2(10)); PROCEDURE get_emp_data (emp_data IN OUT emp_data_type); END; CREATE OR REPLACE PACKAGE BODY emp_package AS PROCEDURE get_emp_data (emp_data IN OUT emp_data_type) IS BEGIN SELECT empno, ename, to_char(hiredate, 'DD/MON/YY') INTO emp_data FROM emp WHERE empno = emp_data.emp_number; END;
If the package specification is changed so that the record's field names are changed, but the types remain the same, this does not affect the signature. For example, the following package specification has the same signature as the previous package specification example:
CREATE OR REPLACE PACKAGE emp_package AS TYPE emp_data_type IS RECORD ( emp_num NUMBER, -- was emp_number hire_dat VARCHAR2(12), --was hire_date empname VARCHAR2(10)); -- was emp_name PROCEDURE get_emp_data (emp_data IN OUT emp_data_type); END;
Changing the name of the type of a parameter does not cause a change in the signature if the type remains the same as before. For example, the following package specification for EMP_PACKAGE is the same as the first one on page 10-23:
CREATE OR REPLACE PACKAGE emp_package AS TYPE emp_data_record_type IS RECORD ( emp_number NUMBER, hire_date VARCHAR2(12), emp_name VARCHAR2(10)); PROCEDURE get_emp_data (emp_data IN OUT emp_data_record_type); END;
Whether the timestamp or the signature dependency model is in effect is controlled by the dynamic initialization parameter REMOTE_DEPENDENCIES_MODE.
REMOTE_DEPENDENCIES_MODE = TIMESTAMP
and this is not explicitly overridden dynamically, then only timestamps are used to resolve dependencies.
REMOTE_DEPENDENCIES_MODE = SIGNATURE
ALTER SESSION SET REMOTE_DEPENDENCIES_MODE = {SIGNATURE | TIMESTAMP}
to alter the dependency model for the current session, or
ALTER SYSTEM SET REMOTE_DEPENDENCIES_MODE = {SIGNATURE | TIMESTAMP}
If the REMOTE_DEPENDENCIES_MODE parameter is not specified, either in the INIT.ORA parameter file, or using the ALTER SESSION or ALTER SYSTEM DDL commands, TIMESTAMP is the default value. So, unless you explicitly use the REMOTE_DEPENDENCIES_MODE parameter, or the appropriate DDL command, your server is operating using the timestamp dependency model.
When you use REMOTE_DEPENDENCIES_MODE=SIGNATURE you should be aware of the following:
TIMESTAMP mode, this rebinding does not happen under the SIGNATURE mode, because the local procedure does not get invalidated. You must recompile the local procedure manually to achieve the new rebinding.
When REMOTE_DEPENDENCIES_MODE = TIMESTAMP (the default value), dependencies among library units are handled by comparing timestamps at runtime. If the timestamp of a called remote procedure does not match the timestamp of the called procedure, the calling (dependent) unit is invalidated, and must be recompiled. In this case, if there is no local PL/SQL compiler, the calling application cannot proceed.
In the timestamp dependency mode, signatures are not compared. If there is a local PL/SQL compiler, recompilation happens automatically when the calling procedure is executed.
When REMOTE_DEPENDENCIES_MODE = SIGNATURE, the recorded timestamp in the calling unit is first compared to the current timestamp in the called remote unit. If they match, then the call proceeds normally. If the timestamps do not match, then the signature of the called remote subprogram, as recorded in the calling subprogram, is compared with the current signature of the called subprogram. If they do not match, using the criteria described in the section "What Is a Signature?" on page 10-20, then an error is returned to the calling session.
Oracle recommends that you follow these guidelines for setting the REMOTE_DEPENDENCIES_MODE parameter:
TIMESTAMP (or let it default to that) to get the timestamp dependency mode.
SIGNATURE. This allows
SIGNATURE mode on the server side, make sure to add new procedures to the end of the procedure (or function) declarations in a package spec. Adding a new procedure in the middle of the list of declarations can cause unnecessary invalidation and recompilation of dependent procedures.
Cursor variables are references to cursors. A cursor is a static object; a cursor variable is a pointer to a cursor. Since cursor variables are pointers, they can be passed and returned as parameters to procedures and functions. A cursor variable can also refer to ("point to") different cursors in its lifetime.
Some additional advantages of cursor variables are
See the PL/SQL User's Guide and Reference for a complete discussion of cursor variables.
You normally allocate memory for a cursor variable in the client application, using the appropriate ALLOCATE command. In Pro*C, you use the EXEC SQL ALLOCATE <cursor_name> command. In the OCI, you use the Cursor Data Area.
You can also use cursor variables in applications that run entirely in a single server session. You can declare cursor variables in PL/SQL subprograms, open them, and use them as parameters for other PL/SQL subprograms.
This section includes several examples of cursor variable usage in PL/SQL. For additional cursor variable examples that use the programmatic interfaces, see the following manuals:
The following package defines a PL/SQL cursor variable type EMP_VAL_CV_TYPE, and two procedures. The first procedure opens the cursor variable, using a bind variable in the WHERE clause. The second procedure (FETCH_EMP_DATA) fetches rows from the EMP table using the cursor variable.
CREATE OR REPLACE PACKAGE emp_data AS TYPE emp_val_cv_type IS REF CURSOR RETURN emp%ROWTYPE; PROCEDURE open_emp_cv (emp_cv IN OUT emp_val_cv_type, dept_number IN INTEGER); PROCEDURE fetch_emp_data (emp_cv IN emp_val_cv_type, emp_row OUT emp%ROWTYPE); END emp_data; CREATE OR REPLACE PACKAGE BODY emp_data AS PROCEDURE open_emp_cv (emp_cv IN OUT emp_val_cv_type, dept_number IN INTEGER) IS BEGIN OPEN emp_cv FOR SELECT * FROM emp WHERE deptno = dept_number; END open_emp_cv; PROCEDURE fetch_emp_data (emp_cv IN emp_val_cv_type, emp_row OUT emp%ROWTYPE) IS BEGIN FETCH emp_cv INTO emp_row; END fetch_emp_data; END emp_data;
The following example shows how you can call the EMP_DATA package procedures from a PL/SQL block:
DECLARE -- declare a cursor variable emp_curs emp_data.emp_val_cv_type; dept_number dept.deptno%TYPE; emp_row emp%ROWTYPE; BEGIN dept_number := 20; -- open the cursor using a variable emp_data.open_emp_cv(emp_curs, dept_number); -- fetch the data and display it LOOP emp_data.fetch_emp_data(emp_curs, emp_row); EXIT WHEN emp_curs%NOTFOUND; DBMS_OUTPUT.PUT(emp_row.ename || ' '); DBMS_OUTPUT.PUT_LINE(emp_row.sal); END LOOP; END;
The power of cursor variables comes from their ability to point to different cursors. In the following package example, a discriminant is used to open a cursor variable to point to one of two different cursors:
CREATE OR REPLACE PACKAGE emp_dept_data AS TYPE cv_type IS REF CURSOR; PROCEDURE open_cv (cv IN OUT cv_type, discrim IN POSITIVE); END emp_dept_data; / CREATE OR REPLACE PACKAGE BODY emp_dept_data AS PROCEDURE open_cv (cv IN OUT cv_type, discrim IN POSITIVE) IS BEGIN IF discrim = 1 THEN OPEN cv FOR SELECT * FROM emp WHERE sal > 2000; ELSIF discrim = 2 THEN OPEN cv FOR SELECT * FROM dept; END IF; END open_cv; END emp_dept_data;
You can call the OPEN_CV procedure to open the cursor variable and point it to either a query on the EMP table or on the DEPT table. How would you use this? The following PL/SQL block shows that you can fetch using the cursor variable, then use the ROWTYPE_MISMATCH predefined exception to handle either fetch:
DECLARE emp_rec emp%ROWTYPE; dept_rec dept%ROWTYPE; cv emp_dept_data.cv_type; BEGIN emp_dept_data.open_cv(cv, 1); -- open CV for EMP fetch FETCH cv INTO dept_rec; -- but fetch into DEPT record -- which raises ROWTYPE_MISMATCH DBMS_OUTPUT.PUT(dept_rec.deptno); DBMS_OUTPUT.PUT_LINE(' ' || dept_rec.loc); EXCEPTION WHEN ROWTYPE_MISMATCH THEN BEGIN DBMS_OUTPUT.PUT_LINE ('Row type mismatch, fetching EMP data...'); FETCH cv into emp_rec; DBMS_OUTPUT.PUT(emp_rec.deptno); DBMS_OUTPUT.PUT_LINE(' ' || emp_rec.ename); END; END;
You can deliver your stored procedures in object code format using the PL/SQL Wrapper. Wrapping your PL/SQL code hides your application internals. To run the PL/SQL Wrapper, enter the WRAP command at your system prompt using the following syntax:
WRAP INAME=input_file [ONAME=ouput_file]
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See Also:
For complete instructions on using the PL/SQL Wrapper, see the PL/SQL User's Guide and Reference. |
Oracle allows user-defined errors in PL/SQL code to be handled so that user-specified error numbers and messages are returned to the client application. Once received, the client application can handle the error based on the user-specified error number and message returned by Oracle.
User-specified error messages are returned using the RAISE_APPLICATION_ERROR procedure:
RAISE_APPLICATION_ERROR(error_number, 'text', keep_error_stack)
This procedure terminates procedure execution, rolls back any effects of the procedure, and returns a user-specified error number and message (unless the error is trapped by an exception handler). ERROR_NUMBER must be in the range of -20000 to -20999. Error number -20000 should be used as a generic number for messages where it is important to relay information to the user, but having a unique error number is not required. TEXT must be a character expression, 2 Kbytes or less (longer messages are ignored). KEEP_ERROR_STACK can be TRUE, if you want to add the error to any already on the stack, or FALSE, if you want to replace the existing errors. By default, this option is FALSE.
The RAISE_APPLICATION_ERROR procedure is often used in exception handlers or in the logic of PL/SQL code. For example, the following exception handler selects the string for the associated user-defined error message and calls the RAISE_APPLICATION_ERROR procedure:
... WHEN NO_DATA_FOUND THEN SELECT error_string INTO message FROM error_table, V$NLS_PARAMETERS V WHERE error_number = -20101 AND LANG = v.value AND v.name = "NLS_LANGUAGE"; raise_application_error(-20101, message); ...
Several examples earlier in this chapter also demonstrate the use of the RAISE_APPLICATION_ERROR procedure. The next section has an example of passing a user-specified error number from a trigger to a procedure. For information on exception handling when calling remote procedures, see "Handling Errors in Remote Procedures" on page 10-35.
User-defined exceptions are explicitly defined and signaled within the PL/SQL block to control processing of errors specific to the application. When an exception is raised (signaled), the normal execution of the PL/SQL block stops and a routine called an exception handler is invoked. Specific exception handlers can be written to handle any internal or user-defined exception.
Application code can check for a condition that requires special attention using an IF statement. If there is an error condition, two options are available:
RAISE statement that names the appropriate exception. A RAISE statement stops the execution of the procedure and control passes to an exception handler (if any).
RAISE_APPLICATION_ERROR procedure to return a user-specified error number and message.
You can also define an exception handler to handle user-specified error messages. For example, Figure 10-2 illustrates
Declare a user-defined exception in a procedure or package body (private exceptions) or in the specification of a package (public exceptions). Define an exception handler in the body of a procedure (stand-alone or package).
In database PL/SQL program units, an unhandled user-error condition or internal error condition that is not trapped by an appropriate exception handler causes the implicit rollback of the program unit. If the program unit includes a COMMIT statement before the point at which the unhandled exception is observed, the implicit rollback of the program unit can only be completed back to the previous commit.
Additionally, unhandled exceptions in database-stored PL/SQL program units propagate back to client-side applications that call the containing program unit. In such an application, only the application program unit call is rolled back (not the entire application program unit) because it is submitted to the database as a SQL statement.
If unhandled exceptions in database PL/SQL program units are propagated back to database applications, the database PL/SQL code should be modified to handle the exceptions. Your application can also trap for unhandled exceptions when calling database program units and handle such errors appropriately. For more information, see "Handling Errors in Remote Procedures" on page 10-35.
You can use a trigger or stored procedure to create a distributed query. This distributed query is decomposed by the local Oracle into a corresponding number of remote queries, which are sent to the remote nodes for execution. The remote nodes execute the queries and send the results back to the local node. The local node then performs any necessary post-processing and returns the results to the user or application.
If a portion of a distributed statement fails, for example, due to an integrity constraint violation, Oracle returns error number ORA-02055. Subsequent statements or procedure calls return error number ORA-02067 until a rollback or rollback to savepoint is issued.
You should design your application to check for any returned error messages that indicate that a portion of the distributed update has failed. If you detect a failure, you should rollback the entire transaction (or rollback to a savepoint) before allowing the application to proceed.
When a procedure is executed locally or at a remote location, four types of exceptions can occur:
EXCEPTION
NO_DATA_FOUND
ORA-00900 and ORA-02015
RAISE_APPLICATION_ERROR() procedure
When using local procedures, all of these messages can be trapped by writing an exception handler, such as shown in the following example:
EXCEPTION WHEN ZERO_DIVIDE THEN /* ...handle the exception */
Notice that the WHEN clause requires an exception name. If the exception that is raised does not have a name, such as those generated with RAISE_APPLICATION_ERROR, one can be assigned using PRAGMA_EXCEPTION_INIT, as shown in the following example:
DECLARE ... null_salary EXCEPTION; PRAGMA EXCEPTION_INIT(null_salary, -20101); BEGIN ... RAISE_APPLICATION_ERROR(-20101, 'salary is missing'); ... EXCEPTION WHEN null_salary THEN ...
When calling a remote procedure, exceptions are also handled by creating a local exception handler. The remote procedure must return an error number to the local, calling procedure, which then handles the exception as shown in the previous example. Because PL/SQL user-defined exceptions always return ORA-06510 to the local procedure, these exceptions cannot be handled. All other remote exceptions can be handled in the same manner as local exceptions.
When you use SQL*Plus to submit PL/SQL code, and the code contains errors, you receive notification that compilation errors have occurred, but no immediate indication of what the errors are. For example, if you submit a stand-alone (or stored) procedure PROC1 in the file proc1.sql as follows:
SVRMGR> @proc1
and there are one or more errors in the code, you receive a notice such as
MGR-00072: Warning: Procedure PROC1 created with compilation errors
In this case, use the SHOW ERRORS command in SQL*Plus to get a list of the errors that were found. SHOW ERRORS with no argument lists the errors from the most recent compilation. You can qualify SHOW ERRORS using the name of a procedure, function, package, or package body:
SQL> SHOW ERRORS PROC1 SQL> SHOW ERRORS PROCEDURE PROC1
See the SQL*Plus User's Guide and Reference for complete information about the SHOW ERRORS command.
For example, assume you want to create a simple procedure that deletes records from the employee table using SQL*Plus:
CREATE PROCEDURE fire_emp(emp_id NUMBER) AS BEGIN DELETE FROM emp WHER empno = emp_id; END /
Notice that the CREATE PROCEDURE statement has two errors: the DELETE statement has an error (the 'E' is absent from WHERE) and the semicolon is missing after END.
After the CREATE PROCEDURE statement is issued and an error is returned, a SHOW ERRORS statement would return the following lines:
SHOW ERRORS; ERRORS FOR PROCEDURE FIRE_EMP: LINE/COL ERROR -------------- -------------------------------------------- 3/27 PL/SQL-00103: Encountered the symbol "EMPNO" wh. . . 5/0 PL/SQL-00103: Encountered the symbol "END" when . . . 2 rows selected.
Notice that each line and column number where errors were found is listed by the SHOW ERRORS command.
Alternatively, you can query the following data dictionary views to list errors when using any tool or application:
The error text associated with the compilation of a procedure is updated when the procedure is replaced, and deleted when the procedure is dropped.
Original source code can be retrieved from the data dictionary using the following views: ALL_SOURCE, USER_SOURCE, and DBA_SOURCE.
You can debug stored procedures and triggers using the DBMS_OUTPUT supplied package. You put PUT and PUT_LINE statements in your code to output the value of variables and expressions to your terminal. See "Output from Stored Procedures and Triggers" on page 12-22 for more information about the DBMS_OUTPUT package.
A more convenient way to debug, if your platform supports it, is to use the Oracle Procedure Builder, which is part of the Oracle Developer/2000 tool set. Procedure Builder lets you execute PL/SQL procedures and triggers in a controlled debugging environment, and you can set breakpoints, list the values of variables, and perform other debugging tasks. See the Oracle Procedure Builder Developer's Guide for more information.
Procedures can be invoked from many different environments. For example:
LENGTH or ROUND.
Some common examples of invoking procedures from within these environments follow. For more information, see "Calling Stored Functions from SQL Expressions" on page 10-44.
A procedure or trigger can call another stored procedure. For example, included in the body of one procedure might be the line
. . . sal_raise(emp_id, 200); . . .
This line calls the SAL_RAISE procedure. EMP_ID is a variable within the context of the procedure. Note that recursive procedure calls are allowed within PL/SQL; that is, a procedure can call itself.
A procedure can be invoked interactively from an Oracle tool such as SQL*Plus. For example, to invoke a procedure named SAL_RAISE, owned by you, you can use an anonymous PL/SQL block, as follows:
BEGIN sal_raise(1043, 200); END;
An easier way to execute a block is to use the SQL*Plus command EXECUTE, which effectively wraps BEGIN and END statements around the code you enter. For example:
EXECUTE sal_raise(1043, 200);
Some interactive tools allow session variables to be created. For example, when using SQL*Plus, the following statement creates a session variable:
VARIABLE assigned_empno NUMBER
Once defined, any session variable can be used for the duration of the session. For example, you might execute a function and capture the return value using a session variable:
EXECUTE :assigned_empno := hire_emp('JSMITH', 'President', \ 1032, SYSDATE, 5000, NULL, 10); PRINT assigned_empno; ASSIGNED_EMPNO -------------- 2893
See the SQL*Plus User's Guide and Reference for SQL*Plus information. See your tools manual for information about performing similar operations using your development tool.
A 3GL database application such as a precompiler or OCI application can include a call to a procedure within the code of the application.
To execute a procedure within a PL/SQL block in an application, simply call the procedure. The following line within a PL/SQL block calls the FIRE_EMP procedure:
fire_emp(:empno);
In this case, :EMPNO is a host (bind) variable within the context of the application.
To execute a procedure within the code of a precompiler application, you must use the EXEC call interface. For example, the following statement calls the FIRE_EMP procedure in the code of a precompiler application:
EXEC SQL EXECUTE BEGIN fire_emp(:empno); END; END-EXEC;
:EMPNO is a host (bind) variable.
For more information about calling PL/SQL procedures from within 3GL applications, see the following manuals:
References to procedures and packages are resolved according to the algorithm described in "Name Resolution in SQL Statements" on page 4-46.
If you are the owner of a stand-alone procedure or package, you can execute the stand-alone procedure or packaged procedure, or any public procedure or packaged procedure at any time, as described in the previous sections. If you want to execute a stand-alone or packaged procedure owned by another user, the following conditions apply:
EXECUTE privilege for the stand-alone procedure or package containing the procedure, or have the EXECUTE ANY PROCEDURE system privilege. If you are executing a remote procedure, you must have been granted the EXECUTE privilege or EXECUTE ANY PROCEDURE system privilege directly, not via a role.
EXECUTE jward.fire_emp (1043); EXECUTE jward.hire_fire.fire_emp (1043);
When you invoke a procedure, specify a value or parameter for each of the procedure's arguments. Identify the argument values using either of the following methods, or a combination of both:
For example, these statements each call the procedure UPDATE_SAL to increase the salary of employee number 7369 by 500:
sal_raise(7369, 500); sal_raise(sal_incr=>500, emp_id=>7369); sal_raise(7369, sal_incr=>500);
The first statement identifies the argument values by listing them in the order in which they appear in the procedure specification.
The second statement identifies the argument values by name and in an order different from that of the procedure specification. If you use argument names, you can list the arguments in any order.
The third statement identifies the argument values using a combination of these methods. If you use a combination of order and argument names, values identified in order must precede values identified by name.
If you have used the DEFAULT option to define default values for IN parameters to a subprogram (see the PL/SQL User's Guide and Reference), you can pass different numbers of actual parameters to the 1subprogram, accepting or overriding the default values as you please. If an actual value is not passed, the corresponding default value is used. If you want to assign a value to an argument that occurs after an omitted argument (for which the corresponding default is used), you must explicitly designate the name of the argument, as well as its value.
Invoke remote procedures using an appropriate database link and the procedure's name. The following SQL*Plus statement executes the procedure FIRE_EMP located in the database pointed to by the local database link named NY:
EXECUTE fire_emp@NY(1043);
You must explicitly pass values to all remote procedure parameters even if there are defaults. You cannot access remote package variables and constants.
Remote objects can be referenced within the body of a locally defined procedure. The following procedure deletes a row from the remote employee table:
CREATE PROCEDURE fire_emp(emp_id NUMBER) IS BEGIN DELETE FROM emp@sales WHERE empno = emp_id; END;
The list below explains how to properly call remote procedures, depending on the calling environment.
CREATE PROCEDURE local_procedure(arg1, arg2) AS BEGIN ... remote_procedure@dblink(arg1, arg2); ... END;
REMOTE_PROCEDURE@DBLINK. This would enable you to call the remote procedure from an Oracle tool application, such as a SQL*Forms application, as well from within a procedure, OCI application, or precompiler application.
CREATE PROCEDURE local_procedure(arg1, arg2) AS BEGIN ... synonym(arg1, arg2); ... END;
BEGIN local_procedure(arg1, arg2); END;
All calls to remotely stored procedures are assumed to perform updates; therefore, this type of referencing always requires two-phase commit of that transaction (even if the remote procedure is read-only). Furthermore, if a transaction that includes a remote procedure call is rolled back, the work done by the remote procedure is also rolled back. A procedure called remotely cannot execute a COMMIT, ROLLBACK, or SAVEPOINT statement.
A distributed update modifies data on two or more nodes. A distributed update is possible using a procedure that includes two or more remote updates that access data on different nodes. Statements in the construct are sent to the remote nodes and the execution of the construct succeeds or fails as a unit. If part of a distributed update fails and part succeeds, a rollback (of the entire transaction or to a savepoint) is required to proceed. Consider this when creating procedures that perform distributed updates.
Pay special attention when using a local procedure that calls a remote procedure. If a timestamp mismatch is found during execution of the local procedure, the remote procedure is not executed and the local procedure is invalidated.
Synonyms can be created for stand-alone procedures and packages to
When a privileged user needs to invoke a procedure, an associated synonym can be used. Because the procedures defined within a package are not individual objects (that is, the package is the object), synonyms cannot be created for individual procedures within a package.
You can include user-written PL/SQL functions in SQL expressions. (You must be using PL/SQL release 2.1 or greater.) By using PL/SQL functions in SQL statements, you can do the following:
WHERE clause of a query can filter data using criteria that would otherwise have to be evaluated by the application.
PL/SQL functions must be created as top-level functions or declared within a package specification before they can be named within a SQL statement. Stored PL/SQL functions are used in the same manner as built-in Oracle functions (such as SUBSTR or ABS).
PL/SQL functions can be placed wherever an Oracle function can be placed within a SQL statement; that is, wherever expressions can occur in SQL. For example, they can be called from the following:
SELECT command
WHERE and HAVING clause
CONNECT BY, START WITH, ORDER BY, and GROUP BY clauses
VALUES clause of the INSERT command
SET clause of the UPDATE command
You cannot call stored PL/SQL functions from a CHECK constraint clause of a CREATE or ALTER TABLE command or use them to specify a default value for a column. These situations require an unchanging definition.
Use the following syntax to reference a PL/SQL function from SQL:
[[schema.]package.]function_name[@dblink][(param_1...param_n)]
For example, to reference a function that you have created that is called MY_FUNC, in the MY_FUNCS_PKG package, in the SCOTT schema, and that takes two numeric parameters, you could call it as:
SELECT scott.my_funcs_pkg.my_func(10,20) from dual
If only one of the optional schema or package names is given, the first identifier can be either a schema name or a package name. For example, to determine whether PAYROLL in the reference PAYROLL.TAX_RATE is a schema or package name, Oracle proceeds as follows:
PAYROLL package in the current schema.
PAYROLL package is not found, Oracle looks for a schema named PAYROLL that contains a top-level TAX_RATE function. If the TAX_RATE function is not found in the PAYROLL schema, an error message is returned.
PAYROLL package is found in the current schema, Oracle looks for a TAX_RATE function in the PAYROLL package. If a TAX_RATE function is not found in the PAYROLL package, an error message is returned.
You can also refer to a stored top-level function using any synonym that you have defined for it.
In SQL statements, the names of database columns take precedence over the names of functions with no parameters. For example, if schema SCOTT creates the following two objects:
CREATE TABLE emp(new_sal NUMBER ...); CREATE FUNCTION new_sal RETURN NUMBER IS ...;
Then in the following two statements, the reference to NEW_SAL refers to the column EMP.NEW_SAL:
SELECT new_sal FROM emp; SELECT emp.new_sal FROM emp;
To access the function NEW_SAL, you would enter the following:
SELECT scott.new_sal FROM emp;
For example, to call the TAX_RATE PL/SQL function from schema SCOTT, execute it against the SS_NO and SAL columns in TAX_TABLE, and place the results in the variable INCOME_TAX, specify the following:
SELECT scott.tax_rate (ss_no, sal) INTO income_tax FROM tax_table WHERE ss_no = tax_id;
These sample calls to PL/SQL functions are allowed in SQL expressions:
circle_area(radius) payroll.tax_rate(empno) scott.payroll.tax_rate(dependents, empno)@ny
To pass any number of arguments to a function, supply the arguments within the parentheses. You must use positional notation; named notation is not currently supported. For functions that do not accept arguments, omit the parentheses.
The argument's datatypes and the function's return type are limited to those types that are supported by SQL. For example, you cannot call a PL/SQL function that returns a PL/SQL BINARY_INTEGER from a SQL statement.
The stored function gross_pay initializes two of its formal parameters to default values using the DEFAULT clause, as follows:
CREATE FUNCTION gross_pay (emp_id IN NUMBER, st_hrs IN NUMBER DEFAULT 40, ot_hrs IN NUMBER DEFAULT 0) RETURN NUMBER AS ...
When calling gross_pay from a procedural statement, you can always accept the default value of st_hrs. That is because you can use named notation, which lets you skip parameters, as in:
IF gross_pay(eenum,ot_hrs => otime) > pay_limit THEN ...
However, when calling gross_pay from a SQL expression, you cannot accept the default value of st_hrs unless you accept the default value of ot_hrs. That is because you cannot use named notation.
To be callable from SQL expressions, a user-defined PL/SQL function must meet the following basic requirements:
IN parameters; none can be an OUT or IN OUT parameter.
CHAR, DATE, or NUMBER, not PL/SQL types such as BOOLEAN, RECORD, or TABLE.
For example, the following stored function meets the basic requirements:
CREATE FUNCTION gross_pay (emp_id IN NUMBER, st_hrs IN NUMBER DEFAULT 40, ot_hrs IN NUMBER DEFAULT 0) RETURN NUMBER AS st_rate NUMBER; ot_rate NUMBER; BEGIN SELECT srate, orate INTO st_rate, ot_rate FROM payroll WHERE acctno = emp_id; RETURN st_hrs * st_rate + ot_hrs * ot_rate; END gross_pay;
To execute a SQL statement that calls a stored function, the Oracle Server must know the purity level of the function, that is, the extent to which the function is free of side effects. In this context, side effects are references to database tables or packaged variables.
Side effects can prevent the parallelization of a query, yield order-dependent (and therefore indeterminate) results, or require that package state be maintained across user sessions (which is not allowed). Therefore, the following rules apply to stored functions called from SQL expressions:
INSERT, UPDATE, or DELETE statement.
SELECT, VALUES, or SET clause can write the values of packaged variables.
SELECT operation, which can include function calls.)
For stand-alone functions, Oracle can enforce these rules by checking the function body. However, the body of a packaged function is hidden; only its specification is visible. So, for packaged functions, you must use the pragma (compiler directive) RESTRICT_REFERENCES to enforce the rules.
The pragma tells the PL/SQL compiler to deny the packaged function read/write access to database tables, packaged variables, or both. If you try to compile a function body that violates the pragma, you get a compilation error.
To call a packaged function from SQL expressions, you must assert its purity level by coding the pragma RESTRICT_REFERENCES in the package specification (not in the package body). The pragma must follow the function declaration but need not follow it immediately. Only one pragma can reference a given function declaration.
To code the pragma RESTRICT_REFERENCES, you use the syntax
PRAGMA RESTRICT_REFERENCES ( function_name, WNDS [, WNPS] [, RNDS] [, RNPS]);
where:
You can pass the arguments in any order, but you must pass the argument WNDS. No argument implies another; for example, RNPS does not imply WNPS.
In the example below, the function compound neither reads nor writes database or package state, so you can assert the maximum purity level. Always assert the highest purity level that a function allows. That way, the PL/SQL compiler will never reject the function unnecessarily.
CREATE PACKAGE finance AS -- package specification ... FUNCTION compound (years IN NUMBER, amount IN NUMBER, rate IN NUMBER) RETURN NUMBER; PRAGMA RESTRICT_REFERENCES (compound, WNDS, WNPS, RNDS, RNPS); END finance; CREATE PACKAGE BODY finance AS --package body ... FUNCTION compound (years IN NUMBER, amount IN NUMBER, rate IN NUMBER) RETURN NUMBER IS BEGIN RETURN amount * POWER((rate / 100) + 1, years); END compound; -- no pragma in package body END finance;
Later, you might call compound from a PL/SQL block, as follows:
BEGIN ... SELECT finance.compound(yrs,amt,rte) -- function call INTO interest FROM accounts WHERE acctno = acct_id;
Packages can have an initialization part, which is hidden in the package body. Typically, the initialization part holds statements that initialize public variables.
In the following example, the SELECT statement initializes the public variable prime_rate:
CREATE PACKAGE loans AS prime_rate REAL; -- public packaged variable ... END loans; CREATE PACKAGE BODY loans AS ... BEGIN -- initialization part SELECT prime INTO prime_rate FROM rates; END loans;
The initialization code is run only once-the first time the package is referenced. If the code reads or writes database state or package state other than its own, it can cause side effects. Moreover, a stored function that references the package (and thereby runs the initialization code) can cause side effects indirectly. So, to call the function from SQL expressions, you must use the pragma RESTRICT_REFERENCES to assert or imply the purity level of the initialization code.
To assert the purity level of the initialization code, you use a variant of the pragma RESTRICT_REFERENCES, in which the function name is replaced by a package name. You code the pragma in the package specification, where it is visible to other users. That way, anyone referencing the package can see the restrictions and conform to them.
To code the variant pragma RESTRICT_REFERENCES, you use the syntax
PRAGMA RESTRICT_REFERENCES ( package_name, WNDS [, WNPS] [, RNDS] [, RNPS]);
where the arguments WNDS, WNPS, RNDS, and RNPS have the usual meaning.
In the example below, the initialization code reads database state and writes package state. However, you can assert WNPS because the code is writing the state of its own package, which is permitted. So, you assert WNDS, WNPS, RNPS-the highest purity level the function allows. (If the public variable prime_rate were in another package, you could not assert WNPS.)
CREATE PACKAGE loans AS PRAGMA RESTRICT_REFERENCES (loans, WNDS, WNPS, RNPS); prime_rate REAL; ... END loans; CREATE PACKAGE BODY loans AS ... BEGIN SELECT prime INTO prime_rate FROM rates; END loans;
You can place the pragma anywhere in the package specification, but placing it at the top (where it stands out) is a good idea.
To imply the purity level of the initialization code, your package must have a RESTRICT_REFERENCES pragma for one of the functions it declares. From the pragma, Oracle can infer the purity level of the initialization code (because the code cannot break any rule enforced by a pragma). In the next example, the pragma for the function discount implies that the purity level of the initialization code is at least WNDS:
CREATE PACKAGE loans AS ... FUNCTION discount (...) RETURN NUMBER; PRAGMA RESTRICT_REFERENCES (discount, WNDS); END loans; ...
To draw an inference, Oracle can combine the assertions of all RESTRICT_REFERENCES pragmas. For example, the following pragmas (combined) imply that the purity level of the initialization code is at least WNDS, RNDS:
CREATE PACKAGE loans AS ... FUNCTION discount (...) RETURN NUMBER; FUNCTION credit_ok (...) RETURN CHAR; PRAGMA RESTRICT_REFERENCES (discount, WNDS); PRAGMA RESTRICT_REFERENCES (credit_ok, RNDS); END loans; ...
To call a packaged function from SQL expressions, you must assert its purity level using the pragma RESTRICT_REFERENCES. However, if the package has an initialization part, the PL/SQL compiler might not let you assert the highest purity level the function allows. As a result, you might be unable to call the function remotely, in parallel, or from certain SQL clauses.
This happens when a packaged function is purer than the package initialization code. Remember, the first time a package is referenced,
its initialization code is run. If that reference is a function call, any additional side effects caused by the initialization code occur during the call. So, in effect, the initialization code lowers the purity level of the function.
To avoid this problem, move the package initialization code into a subprogram. That way, your application can run the code explicitly (rather than implicitly during package instantiation) without affecting your packaged functions.
A similar problem arises when a packaged function is purer than a subprogram it calls. This lowers the purity level of the function. Therefore, the RESTRICT_REFERENCES pragma for the function must specify the lower purity level. Otherwise, the PL/SQL compiler will reject the function. In the following example, the compiler rejects the function because its pragma asserts RNDS but the function calls a procedure that reads database state:
CREATE PACKAGE finance AS ... FUNCTION compound (years IN NUMBER, amount IN NUMBER) RETURN NUMBER; PRAGMA RESTRICT_REFERENCES (compound, WNDS, WNPS, RNDS, RNPS); END finance; CREATE PACKAGE BODY finance AS ... FUNCTION compound (years IN NUMBER, amount IN NUMBER) RETURN NUMBER IS rate NUMBER; PROCEDURE calc_loan_rate (loan_rate OUT NUMBER) IS prime_rate REAL; BEGIN SELECT p_rate INTO prime_rate FROM rates; ... END; BEGIN calc_loan_rate(rate); RETURN amount * POWER((rate / 100) + 1, years); END compound; END finance;
PL/SQL lets you overload packaged (but not stand-alone) functions. That is, you can use the same name for different functions if their formal parameters differ in number, order, or datatype family.
However, a RESTRICT_REFERENCES pragma can apply to only one function declaration. So, a pragma that references the name of overloaded functions always applies to the nearest foregoing function declaration.
In the following example, the pragma applies to the second declaration of valid:
CREATE PACKAGE tests AS FUNCTION valid (x NUMBER) RETURN CHAR; FUNCTION valid (x DATE) RETURN CHAR; PRAGMA RESTRICT_REFERENCES (valid, WNDS); ...
PL/SQL packages normally consume user global area (UGA) memory corresponding to the number of package variables and cursors in the package. This limits scalability because the memory increases linearly with the number of users. The solution is to allow some packages to be marked as SERIALLY_REUSABLE (using pragma syntax).
For serially reusable packages, the package global memory is not kept in the UGA per user, but instead it is kept in a small pool and reused for different users. This means that the global memory for such a package is only used within a unit of work. At the end of that unit of work, the memory can therefore be released to the pool to be reused by another user (after running the initialization code for all the global variables).
The unit of work for serially reusable packages is implicitly a CALL to the server, for example, an OCI call to the server, or a PL/SQL client-to-server RPC call or server-to-server RPC call.
The state of a nonreusable package (one not marked SERIALLY_REUSABLE) persists for the lifetime of a session. A package's state includes global variables, cursors, and so on.
The state of a serially reusable package persists only for the lifetime of a CALL to the server. On a subsequent call to the server, if a reference is made to the serially reusable package, Oracle creates a new instantiation (described below) of the serially reusable package and initializes all the global variables to NULL or to the default values provided. Any changes made to the serially reusable package state in the previous CALLs to the server are not visible.
Since the state of a non-reusable package persists for the lifetime of the session, this locks up UGA memory for the whole session. In applications such as Oracle Office a log-on session can typically exist for days together. Applications often need to use certain packages only for certain localized periods in the session and would ideally like to de-instantiate the package state in the middle of the session once they are done using the package.
With SERIALLY_REUSABLE packages the application developers have a way of modelling their applications to manage their memory better for scalability. Package state that they care about only for the duration of a CALL to the server should be captured in SERIALLY_REUSABLE packages.
A package can be marked serially reusable by a pragma. The syntax of the pragma is:
PRAGMA SERIALLY_REUSABLE;
A package specification can be marked serially reusable whether or not it has a corresponding package body. If the package has a body, the body must have the serially reusable pragma if its corresponding specification has the pragma; and it cannot have the serially reusable pragma unless the specification also has the pragma.
A package that is marked SERIALLY_REUSABLE has the following properties:
WORK boundaries, which correspond to CALLs to the server (either OCI call boundaries or PL/SQL RPC calls to the server).
This example has a serially reusable package specification (there is no body). It demonstrates how package variables behave across CALL boundaries.
connect scott/tiger; create or replace package SR_PKG is pragma SERIALLY_REUSABLE; n number := 5; -- default initialization end SR_PKG; /
Suppose your Enterprise Manager (or SQL*Plus) application issues the following:
connect scott/tiger # first CALL to server begin SR_PKG.n := 10; end; / # second CALL to server begin dbms_output.put_line(SR_PKG.n); end; /
The above program will print:
5
This example has both a package specification and body which are serially reusable. Like Example 1, this example demonstrates how the package variables behave across CALL boundaries.
SQL> connect scott/tiger; Connected. SQL> SQL> drop package SR_PKG; Statement processed. SQL> SQL> create or replace package SR_PKG is 2> 3> pragma SERIALLY_REUSABLE; 4> 5> type str_table_type is table of varchar2(200) index by binary_integer; 6> 7> num number := 10; 8> str varchar2(200) := 'default-init-str'; 9> str_tab str_table_type; 10> 11> procedure print_pkg; 12> procedure init_and_print_pkg(n number, v varchar2); 13> 14> end SR_PKG; 15> / Statement processed. SQL> SQL> SQL> create or replace package body SR_PKG is 2> 3> -- the body is required to have the pragma since the 4> -- specification of this package has the pragma 5> pragma SERIALLY_REUSABLE; 6> 7> procedure print_pkg is 8> begin 9> dbms_output.put_line('num: ' || SR_PKG.num); 10> dbms_output.put_line('str: ' || SR_PKG.str); 11> 12> dbms_output.put_line('number of table elems: ' || SR_PKG.str_tab.count); 13> for i in 1..SR_PKG.str_tab.count loop 14> dbms_output.put_line(SR_PKG.str_tab(i)); 15> end loop; 16> end; 17> 18> procedure init_and_print_pkg(n number, v varchar2) is 19> begin 20> 21> -- init the package globals 22> SR_PKG.num := n; 23> SR_PKG.str := v; 24> for i in 1..n loop 25> SR_PKG.str_tab(i) := v || ' ' || i; 26> end loop; 27> 28> -- now print the package 29> print_pkg; 30> end; 31> 32> end SR_PKG; 33> / Statement processed. SQL> show errors; No errors for PACKAGE BODY SR_PKG SQL> SQL> set serveroutput on; Server Output ON SQL> SQL> Rem SR package access in a CALL SQL> begin 2> 3> -- initialize and print the package 4> dbms_output.put_line('Initing and printing pkg state..'); 5> SR_PKG.init_and_print_pkg(4, 'abracadabra'); 6> 7> -- print it in the same call to the server. 8> -- we should see the initialized values. 9> dbms_output.put_line('Printing package state in the same CALL...'); 10> SR_PKG.print_pkg; 11> 12> end; 13> / Statement processed. Initing and printing pkg state.. num: 4 str: abracadabra number of table elems: 4 abracadabra 1 abracadabra 2 abracadabra 3 abracadabra 4 Printing package state in the same CALL... num: 4 str: abracadabra number of table elems: 4 abracadabra 1 abracadabra 2 abracadabra 3 abracadabra 4 SQL> SQL> Rem SR package access in subsequent CALL SQL> begin 2> 3> -- print the package in the next call to the server. 4> -- We should that the package state is reset to the initial (default) values. 5> dbms_output.put_line('Printing package state in the next CALL...'); 6> SR_PKG.print_pkg; 7> 8> end; 9> / Statement processed. Printing package state in the next CALL... num: 10 str: default-init-str number of table elems: 0 SQL>
This example demonstrates that any open cursors in serially reusable packages get closed automatically at the end of a WORK boundary (which is a CALL), and that in a new CALL these cursors need to be opened again.
Rem For serially reusable pkg: At the end work boundaries Rem (which is currently the OCI call boundary) all open Rem cursors will be closed. Rem Rem Since the cursor is closed - every time we fetch we Rem will start at the first row again. SQL> connect scott/tiger; Connected. SQL> SQL> drop package SR_PKG; Statement processed. SQL> drop table people; Statement processed. SQL> SQL> SQL> create table people (name varchar2(20)); Statement processed. SQL> SQL> insert into people values ('ET'); 1 row processed. SQL> insert into people values ('RAMBO'); 1 row processed. SQL> SQL> create or replace package SR_PKG is 2> 3> pragma SERIALLY_REUSABLE; 4> cursor c is select name from people; 5> 6> end SR_PKG; 7> / Statement processed. SQL> show errors; No errors for PACKAGE SR_PKG SQL> SQL> set serveroutput on; Server Output ON SQL> SQL> create or replace procedure fetch_from_cursor is 2> name varchar2(200); 3> begin 4> 5> if (SR_PKG.c%ISOPEN) then 6> dbms_output.put_line('cursor is already open.'); 7> else 8> dbms_output.put_line('cursor is closed; opening now.'); 9> open SR_PKG.c; 10> end if; 11> 12> -- fetching from cursor. 13> fetch SR_PKG.c into name; 14> dbms_output.put_line('fetched: ' || name); 15> 16> fetch SR_PKG.c into name; 17> dbms_output.put_line('fetched: ' || name); 18> 19> -- Oops forgot to close the cursor (SR_PKG.c). 20> -- But, since it is a Serially Reusable pkg's cursor, 21> -- it will be closed at the end of this CALL to the server. 22> 23> end; 24> / Statement processed. SQL> show errors; No errors for PROCEDURE FETCH_FROM_CURSOR SQL> SQL> set serveroutput on; Server Output ON SQL> SQL> execute fetch_from_cursor; Statement processed. cursor is closed; opening now. fetched: ET fetched: RAMBO SQL> SQL> execute fetch_from_cursor; Statement processed. cursor is closed; opening now. fetched: ET fetched: RAMBO SQL> SQL> execute fetch_from_cursor; Statement processed. cursor is closed; opening now. fetched: ET fetched: RAMBO SQL>
To call a PL/SQL function from SQL, you must either own or have EXECUTE privileges on the function. To select from a view defined with a PL/SQL function, you are required to have SELECT privileges on the view. No separate EXECUTE privileges are needed to select from the view.
Several packaged procedures are provided with the Oracle Server, either to extend the functionality of the database or to give PL/SQL access to some SQL features. You may take advantage of the functionality provided by these packages when creating your application, or you may simply want to use these packages for ideas in creating your own stored procedures.
This section lists each of the supplied packages and indicates where they are described in more detail. These packages run as the invoking user rather than the package owner. The packaged procedures are callable through public synonyms of the same name.
Oracle supplies the following packaged procedures to give PL/SQL access to some features of SQL:
Table 10-6 describes each of these packages. The footnotes at the end of Table 10-6 explain any restrictions on the use of each procedure. You should consult the package specifications for the most up-to-date information on these packages.
For more details on each SQL command equivalent, see the Oracle8 SQL Reference.
The COMMIT, ROLLBACK, ROLLBACK... TO SAVEPOINT, and SAVEPOINT procedures are directly supported by PL/SQL; they are included in the DBMS_TRANSACTION package for completeness.
Several packages are supplied with Oracle to extend the functionality of the database (DBMS_* and UTL_* packages). The cross-reference column in Table 10-7 tells you where to look for more information on each of these packages.
You can use the DBMS_DESCRIBE package to get information about a stored procedure or function.
This package provides the same functionality as the Oracle Call Interface OCIDescribeAny() call. The procedure DESCRIBE_PROCEDURE in this package accepts the name of a stored procedure, and a description of the procedure and each of its parameters. For more information on the OCIDescribeAny() call, see the Oracle Call Interface Programmer's Guide.
To create the DBMS_DESCRIBE package, submit the DBMSDESC.SQL and PRVTDESC.PLB scripts when connected as the user SYS. These scripts are run automatically by the CATPROC.SQL script. See "Privileges Required to Execute a Procedure" on page 10-40 for information on the necessary privileges for users who will be executing this package.
This package is available to PUBLIC and performs its own security checking based on the schema object being described.
The DBMS_DESCRIBE package declares two PL/SQL table types, which are used to hold data returned by DESCRIBE_PROCEDURE in its OUT parameters. The types are
TYPE VARCHAR2_TABLE IS TABLE OF VARCHAR2(30)INDEX BY BINARY_INTEGER;TYPE NUMBER_TABLE IS TABLE OF NUMBER INDEX BY BINARY_INTEGER;
DBMS_DESCRIBE can raise application errors in the range -20000 to -20004. The errors are
-20000: ORU 10035: cannot describe a package ('X') only a procedure within a package -20001: ORU-10032: procedure 'X' within package 'Y' does not exist -20002: ORU-10033 object 'X' is remote, cannot describe; expanded name 'Y' -20003: ORU-10036: object 'X' is invalid and cannot be described -20004: syntax error attempting to parse 'X'
The parameters for DESCRIBE_PROCEDURE are shown in Table 10-8. The syntax is:
PROCEDURE DESCRIBE_PROCEDURE( object_name IN VARCHAR2, reserved1 IN VARCHAR2, reserved2 IN VARCHAR2, overload OUT NUMBER_TABLE, position OUT NUMBER_TABLE, level OUT NUMBER_TABLE, argument_name OUT VARCHAR2_TABLE, datatype OUT NUMBER_TABLE, default_value OUT NUMBER_TABLE, in_out OUT NUMBER_TABLE, length OUT NUMBER_TABLE, precision OUT NUMBER_TABLE, scale OUT NUMBER_TABLE, radix OUT NUMBER_TABLE spare OUT NUMBER_TABLE);
All values from DESCRIBE_PROCEDURE are returned in its OUT parameters. The datatypes for these are PL/SQL tables, to accommodate a variable number of parameters.
One use of the DESCRIBE_PROCEDURE procedure would be as an external service interface.
For example, consider a client that provides an OBJECT _NAME of SCOTT.ACCOUNT_UPDATE where ACCOUNT_UPDATE is an overloaded function with specification:
table account (account_no number, person_id number,
balance number(7,2))
table person (person_id number(4), person_nm varchar2(10))
function ACCOUNT_UPDATE (account_no number,
person person%rowtype,
amounts dbms_describe.number_table,
trans_date date)
return accounts.balance%type;
function ACCOUNT_UPDATE (account_no number,
person person%rowtype,
amounts dbms_describe.number_table,
trans_no number)
return accounts.balance%type;
The describe of this procedure might look similar to the output shown below.
overload position argument level datatype length prec scale rad -------- --------- -------- ------ -------- ------ ---- ----- --- 1 0 0 2 22 7 2 10 1 1 ACCOUNT 0 2 0 0 0 0 1 2 PERSON 0 250 0 0 0 0 1 1 PERSON_ID 1 2 22 4 0 10 1 2 PERSON_NM 1 1 10 0 0 0 1 3 AMOUNTS 0 251 0 0 0 0 1 1 1 2 22 0 0 0 1 4 TRANS_DATE 0 12 0 0 0 0 2 0 0 2 22 7 2 10 2 1 ACCOUNT_NO 0 2 22 0 0 0 2 2 PERSON 0 2 22 4 0 10 2 3 AMOUNTS 0 251 22 4 0 10 2 1 1 2 0 0 0 0 2 4 TRANS_NO 0 2 0 0 0 0
The following PL/SQL procedure has as its parameters all of the PL/SQL datatypes:
CREATE OR REPLACE PROCEDURE p1 ( pvc2 IN VARCHAR2, pvc OUT VARCHAR, pstr IN OUT STRING, plong IN LONG, prowid IN ROWID, pchara IN CHARACTER, pchar IN CHAR, praw IN RAW, plraw IN LONG RAW, pbinint IN BINARY_INTEGER, pplsint IN PLS_INTEGER, pbool IN BOOLEAN, pnat IN NATURAL, ppos IN POSITIVE, pposn IN POSITIVEN, pnatn IN NATURALN, pnum IN NUMBER, pintgr IN INTEGER, pint IN INT, psmall IN SMALLINT, pdec IN DECIMAL, preal IN REAL, pfloat IN FLOAT, pnumer IN NUMERIC, pdp IN DOUBLE PRECISION, pdate IN DATE, pmls IN MLSLABEL) AS BEGIN NULL; END;
If you describe this procedure using the package below:
CREATE OR REPLACE PACKAGE describe_it AS PROCEDURE desc_proc (name VARCHAR2); END describe_it; CREATE OR REPLACE PACKAGE BODY describe_it AS PROCEDURE prt_value(val VARCHAR2, isize INTEGER) IS n INTEGER; BEGIN n := isize - LENGTHB(val); IF n < 0 THEN n := 0; END IF; DBMS_OUTPUT.PUT(val); FOR i in 1..n LOOP DBMS_OUTPUT.PUT(' '); END LOOP; END prt_value; PROCEDURE desc_proc (name VARCHAR2) IS overload DBMS_DESCRIBE.NUMBER_TABLE; position DBMS_DESCRIBE.NUMBER_TABLE; c_level DBMS_DESCRIBE.NUMBER_TABLE; arg_name DBMS_DESCRIBE.VARCHAR2_TABLE; dty DBMS_DESCRIBE.NUMBER_TABLE; def_val DBMS_DESCRIBE.NUMBER_TABLE; p_mode DBMS_DESCRIBE.NUMBER_TABLE; length DBMS_DESCRIBE.NUMBER_TABLE; precision DBMS_DESCRIBE.NUMBER_TABLE; scale DBMS_DESCRIBE.NUMBER_TABLE; radix DBMS_DESCRIBE.NUMBER_TABLE; spare DBMS_DESCRIBE.NUMBER_TABLE; idx INTEGER := 0; BEGIN DBMS_DESCRIBE.DESCRIBE_PROCEDURE( name, null, null, overload, position, c_level, arg_name, dty, def_val, p_mode, length, precision, scale, radix, spare); DBMS_OUTPUT.PUT_LINE('Position Name DTY Mode'); LOOP idx := idx + 1; prt_value(TO_CHAR(position(idx)), 12); prt_value(arg_name(idx), 12); prt_value(TO_CHAR(dty(idx)), 5); prt_value(TO_CHAR(p_mode(idx)), 5); DBMS_OUTPUT.NEW_LINE; END LOOP; EXCEPTION WHEN NO_DATA_FOUND THEN DBMS_OUTPUT.NEW_LINE; DBMS_OUTPUT.NEW_LINE; END desc_proc; END describe_it;
Then the results, as shown below, list all the numeric codes for the PL/SQL datatypes:
Position Name Datatype_Code Mode 1 PVC2 1 0 2 PVC 1 1 3 PSTR 1 2 4 PLONG 8 0 5 PROWID 11 0 6 PCHARA 96 0 7 PCHAR 96 0 8 PRAW 23 0 9 PLRAW 24 0 10 PBININT 3 0 11 PPLSINT 3 0 12 PBOOL 252 0 13 PNAT 3 0 14 PPOS 3 0 15 PPOSN 3 0 16 PNATN 3 0 17 PNUM 2 0 18 PINTGR 2 0 19 PINT 2 0 20 PSMALL 2 0 21 PDEC 2 0 22 PREAL 2 0 23 PFLOAT 2 0 24 PNUMER 2 0 25 PDP 2 0 26 PDATE 12 0 27 PMLS 106 0
The following data dictionary views provide information about procedures and packages:
The OBJECT_SIZE views show the sizes of the PL/SQL objects. For a complete description of these data dictionary views, see your Oracle8 Reference.
The following statements are used in Examples 1 through 3:
CREATE PROCEDURE fire_emp(emp_id NUMBER) AS BEGIN DELETE FROM em WHERE empno = emp_id; END; / CREATE PROCEDURE hire_emp (name VARCHAR2, job VARCHAR2, mgr NUMBER, hiredate DATE, sal NUMBER, comm NUMBER, deptno NUMBER) IS BEGIN INSERT INTO emp VALUES (emp_sequence.NEXTVAL, name, job, mgr, hiredate, sal, comm, deptno); END; /
The first CREATE PROCEDURE statement has an error in the DELETE statement. (The 'p' is absent from 'emp'.)
The following query returns all the errors for the objects in the associated schema:
SELECT name, type, line, position, text FROM user_errors;
The following results are returned:
NAME TYPE LIN POS TEXT -------- ---- --- --- ------------------------------------- FIRE_EMP PROC 3 15 PL/SQL-00201: identifier 'EM' must be declared FIRE_EMP PROC 3 3 PL/SQL: SQL Statement ignored
The following query returns the source code for the HIRE_EMP procedure created in the example statement at the beginning of this section:
SELECT line, text FROM user_source WHERE name = 'HIRE_EMP';
The following results are returned:
LINE TEXT ------ ----------------------------------------------------- 1 PROCEDURE hire_emp (name VARCHAR2, job VARCHAR2, 2 mgr NUMBER, hiredate DATE, sal NUMBER, 3 comm NUMBER, deptno NUMBER) 4 IS 5 BEGIN 6 INSERT INTO emp VALUES (emp_seq.NEXTVAL, name, 7 job, mgr, hiredate, sal, comm, deptno); 8 END;
The following query returns information about the amount of space in the SYSTEM tablespace that is required to store the HIRE_EMP procedure:
SELECT name, source_size + parsed_size + code_size + error_size "TOTAL SIZE" FROM user_object_size WHERE name = 'HIRE_EMP';
The following results are returned:
NAME TOTAL SIZE ------------------------------ ---------- HIRE_EMP 3897
The functions in this package let you get the information that you need about ROWIDs. You can find out the data block number, the object number, and other components of the ROWID without having to write code to interpret the base-64 character external ROWID.
The specification for the DBMS_ROWID package is in the file dbmsutil.sql. This package is loaded when you create a database, and run catproc.sql.
Some of the functions in this package take a single parameter: a ROWID. This can be a character or a binary ROWID, either restricted or extended, as required. For each function described in this section, both the parameter types and the return type are described.
You can call the DBMS_ROWID functions and procedures from PL/SQL code, and you can also use the functions in SQL statements.
You can use functions from the DBMS_ROWID package just like any built-in SQL function. That is, you can use them wherever an expression can be used. In this example, the ROWID_BLOCK_NUMBER function is used to return just the block number of a single row in the EMP table:
SELECT dbms_rowid.rowid_block_number(rowid) FROM emp WHERE ename = 'KING';
This example returns the ROWID for a row in the EMP table, extracts the data object number from the ROWID, using the ROWID_OBJECT function in the DBMS_ROWID package, then displays the object number:
DECLARE object_no INTEGER; row_id ROWID; ... BEGIN SELECT ROWID INTO row_id FROM emp WHERE empno = 7499; object_no := dbms_rowid.rowid_object(row_id); dbms_output.put_line('The obj. # is '|| object_no); ...
The DBMS_ROWID package functions and procedures can raise the ROWID_INVALID exception. The exception is defined in the DBMS_ROWID package as:
PRAGMA EXCEPTION_INIT(ROWID_INVALID, -1410);
The ROWID_CREATE function lets you create a ROWID, given the component parts as parameters. This function is mostly useful for testing ROWID operations, since only the Oracle Server can create a valid ROWID that points to data in a database.
FUNCTION DBMS_ROWID.ROWID_CREATE( rowid_type IN NUMBER, object_number IN NUMBER, relative_fno IN NUMBER, block_number IN NUMBER, row_number IN NUMBER) RETURN ROWID;
Set the ROWID_TYPE parameter to 0 for a restricted ROWID, and to 1 to create an extended ROWID.
If you specify ROWID_TYPE as 0, the required OBJECT_NUMBER parameter is ignored, and ROWID_CREATE returns a restricted ROWID.
Create a dummy extended ROWID:
my_rowid := DBMS_ROWID.ROWID_CREATE(1, 9999, 12, 1000, 13);
Find out what the ROWID_OBJECT function returns:
obj_number := DBMS_ROWID.ROWID_OBJECT(my_rowid);
The variable OBJ_NUMBER now contains 9999.
This procedure returns information about a ROWID, including its type (restricted or extended), and the components of the ROWID. This is a procedure, and cannot be used in a SQL statement.
DBMS_ROWID.ROWID_INFO( rowid_in IN ROWID, rowid_type OUT NUMBER, object_number OUT NUMBER, relative_fno OUT NUMBER, block_number OUT NUMBER, row_number OUT NUMBER);
The IN parameter ROWID_IN determines if the ROWID is a restricted (0) or extended (1) ROWID.
The OUT parameters return the information about the ROWID, as indicated by their names.
For information about the ROWID_TYPE parameter, see the ROWID_TYPE function on page 10-86.
To read back the values for the ROWID that you created in the ROWID_CREATE example:
DBMS_ROWID.ROWID_INFO(my_rowid, rid_type, obj_num, file_num, block_num, row_num); DBMS_OUTPUT.PUT_LINE('The type is ' || rid_type); DBMS_OUTPUT.PUT_LINE('Data object number is ' || obj_num); -- and so on...
This function returns 0 if the ROWID is a restricted ROWID, and 1 if it is extended.
FUNCTION DBMS_ROWID.ROWID_TYPE(rowid_val IN ROWID) RETURN NUMBER;
IF DBMS_ROWID.ROWID_TYPE(my_rowid) = 1 THEN my_obj_num := DBMS_ROWID.ROWID_OBJECT(my_rowid);
This function returns the data object number for an extended ROWID. The function returns zero if the input ROWID is a restricted ROWID.
DBMS_ROWID.ROWID_OBJECT(rowid_val IN ROWID) RETURN NUMBER;
SELECT dbms_rowid.rowid_object(ROWID) FROM emp WHERE empno = 7499;
This function returns the relative file number of the ROWID specified as the IN parameter. (The file number is relative to the tablespace.)
DBMS_ROWID.ROWID_RELATIVE_FNO(rowid_val IN ROWID) RETURN NUMBER;
The example PL/SQL code fragment returns the relative file number:
DECLARE file_number INTEGER; rowid_val ROWID; BEGIN SELECT ROWID INTO rowid_val FROM dept WHERE loc = 'Boston'; file_number := dbms_rowid.rowid_relative_fno(rowid_val); ...
This function returns the database block number for the input ROWID.
DBMS_ROWID.ROWID_BLOCK_NUMBER(rowid_val IN ROWID) RETURN NUMBER;
The example SQL statement selects the block number from a ROWID and inserts it into another table:
INSERT INTO T2 (SELECT dbms_rowid.rowid_block_number(ROWID) FROM some_table WHERE key_value = 42);
This function extracts the row number from the ROWID IN parameter.
DBMS_ROWID.ROWID_ROW_NUMBER(rowid_val IN ROWID) RETURN NUMBER;
Select a row number:
SELECT dbms_rowid.rowid_row_number(ROWID) FROM emp WHERE ename = 'ALLEN';
This function extracts the absolute file number from a ROWID, where the file number is absolute for a row in a given schema and table. The schema name and the name of the schema object (such as a table name) are provided as IN parameters for this function.
DBMS_ROWID.ROWID_TO_ABSOLUTE_FNO( rowid_val IN ROWID, schema_name IN VARCHAR2, object_name IN VARCHAR2) RETURN NUMBER;
DECLARE rel_fno INTEGER; rowid_val CHAR(18); object_name VARCHAR2(20) := 'EMP'; BEGIN SELECT ROWID INTO rowid_val FROM emp WHERE empno = 9999; rel_fno := dbms_rowid.rowid_to_absolute_fno( rowid_val, 'SCOTT', object_name);
This function translates a restricted ROWID that addresses a row in a schema and table that you specify to the extended ROWID format.
DBMS_ROWID.ROWID_TO_EXTENDED( restr_rowid IN ROWID, schema_name IN VARCHAR2, object_name IN VARCHAR2) RETURN ROWID;
Assume that there is a table called RIDS in the schema SCOTT, and that the table contains a column ROWID_COL that holds ROWIDs (restricted), and a column TABLE_COL that point to other tables in the SCOTT schema. You can convert the ROWIDs to extended format with the statement:
UPDATE SCOTT.RIDS SET rowid_col = dbms_rowid.rowid_to_extended(rowid_col, 'SCOTT", TABLE_COL);
ROWID_TO_EXTENDED returns the ROWID in the extended character format. If the input ROWID is NULL, the function returns NULL. If a zero-valued ROWID is supplied (00000000.0000.0000), a zero-valued restricted ROWID is returned.
If the schema and object names are provided as IN parameters, this function verifies SELECT authority on the table named, and converts the restricted ROWID provided to an extended ROWID, using the data object number of the table. That ROWID_TO_EXTENDED returns a value, however, does not guarantee that the converted ROWID actually references a valid row in the table, either at the time that the function is called, or when the extended ROWID is actually used.
If the schema and object name are not provided (are passed as NULL), then this function attempts to fetch the page specified by the restricted ROWID provided. It treats the file number stored in this ROWID as the absolute file number. This can cause problems if the file has been dropped, and its number has been reused prior to the migration. If the fetched page belongs to a valid table, the data object number of this table is used in converting to an extended ROWID value. This is very inefficient, and Oracle recommends doing this only as a last resort, when the target table is not known. The user must still know the correct table name at the time of using the converted value.
If an extended ROWID value is supplied, the data object number in the input extended ROWID is verified against the data object number computed from the table name parameter. If the two numbers do not match, the INVALID_ROWID exception is raised. If they do match, the input ROWID is returned.
See the ROWID_VERIFY function on page 10-90 for a method to determine if a given ROWID can be converted to the extended format.
This function converts an extended ROWID into restricted ROWID format.
DBMS_ROWID.ROWID_TO_RESTRICTED(ext_rowid IN ROWID) RETURN ROWID;
INSERT INTO RID_T2@V7db1 SELECT dbms_rowid.rowid_to_restricted(ROWID) FROM scott.emp@O8db1 WHERE ename = 'SMITH';
This function returns 0 if the input restricted ROWID can be converted to extended format, given the input schema name and table name, and it returns 1 if the conversion is not possible. Note that you can use this function in a BOOLEAN context in a SQL statement, as shown in the example.
DBMS_ROWID.ROWID_VERIFY( restr_rowid IN ROWID, schema_name IN VARCHAR2, object_name IN VARCHAR2) RETURN ROWID;
Considering the schema in the example for the ROWID_TO_EXTENDED function on page 10-88, you can use the following statement to find bad ROWIDs prior to conversion:
SELECT ROWID, rowid_col FROM SCOTT.RIDS WHERE dbms_rowid.rowid_verify(rowid_col, NULL, NULL);
The stored package UTL_HTTP makes HTTP (hyper-text transfer protocol) callouts from PL/SQL and SQL. You can use it to access data on the internet, or to call Oracle Web Server Cartridges. The package contains two similar entrypoints, each of which takes a string URL (universal resource locator), contacts that site, and returns the data (typically HTML - hyper-text markup language) obtained from that site.
This is the specification of packaged function UTL_HTTP.REQUEST:
function request (url in varchar2) return varchar2;
UTL_HTTP.REQUEST returns up to the first 2000 bytes of the data retrieved from the given URL. For example:
SVRMGR> select utl_http.request('http://www.oracle.com/') from dual; UTL_HTTP.REQUEST('HTTP://WWW.ORACLE.COM/') ------------------------------------------------------------------- <html> <head><title>Oracle Corporation Home Page</title> <!--changed Jan. 16, 19 1 row selected.
This is the specification of packaged function UTL_HTTP.REQUEST_PIECES, which uses type UTL_HTTP.HTML_PIECES:
type html_pieces is table of varchar2(2000) index by binary_integer; function request_pieces (url in varchar2, max_pieces natural default 32767) return html_pieces;
UTL_HTTP.REQUEST_PIECES returns a PL/SQL-table of 2000-byte pieces of the data retrieved from the given URL. The optional second argument places a bound on the number of pieces retrieved. For example, the following block retrieves up to 100 pieces of data (each 2000 bytes, except perhaps the last) from the URL. It prints the number of pieces retrieved and the total length, in bytes, of the data retrieved.
set serveroutput on / declare x utl_http.html_pieces; begin x := utl_http.request_pieces('http://www.oracle.com/', 100); dbms_output.put_line(x.count || ' pieces were retrieved.'); dbms_output.put_line('with total length '); if x.count < 1 then dbms_output.put_line('0'); else dbms_output.put_line ((2000 * (x.count - 1)) + length(x(x.count))); end if; end; /
Here is the output:
Statement processed. 4 pieces were retrieved. with total length 7687
Below is the specification for package UTL_HTTP. It describes the exceptions that can be raised by functions REQUEST and REQUEST_PIECES:
create or replace package utl_http is -- Package UTL_HTTP contains functions REQUEST and REQUEST_PIECES for -- making HTTP callouts from PLSQL programs. -- Function REQUEST takes a URL as its argument. Its return-type is a -- string of length 2000 or less, which contains up to the first 2000 bytes -- of the html result returned from the HTTP request to the argument URL. function request (url in varchar2) return varchar2; pragma restrict_references (request, wnds, rnds, wnps, rnps); -- Function REQUEST_PIECES also takes a URL as its argument. Its -- return-type is a PLSQL-table of type UTL_HTTP.HTML_PIECES. Each -- element of that PLSQL-table is a string of length 2000. The -- final element may be shorter than 2000 characters. type html_pieces is table of varchar2(2000) index by binary_integer; function request_pieces (url in varchar2, max_pieces natural default 32767) return html_pieces; pragma restrict_references (request_pieces, wnds, rnds, wnps, rnps); -- The elements of the PLSQL-table returned by REQUEST_PIECES are -- successive pieces of the data obtained from the HTTP request to that -- URL. Here is a typical URL: -- http://www.oracle.com -- So a call to REQUEST_PIECES could look like the example below. Note the -- use of the plsql-table method COUNT to discover the number of pieces -- returned, which may be zero or more: -- -- declare pieces utl_http.html_pieces; -- begin -- pieces := utl_http.request_pieces('http://www.oracle.com/'); -- for i in 1 .. pieces.count loop -- .... -- process each piece -- end loop; -- end; -- -- The second argument to REQUEST_PIECES, "MAX_PIECES", is optional. It is -- the maximum number of pieces (each 2000 characters in length, except for -- the last, which may be shorter), that REQUEST_PIECES should return. If -- provided, that argument should be a positive integer. -- Exceptional conditions: -- If initialization of the http-callout subsystem fails (for -- environmental reasons, for example, lack of available memory) -- then exception UTL_HTTP.INIT_FAILED is raised: init_failed exception; -- When the HTTP call fails (e.g., because of failure of the HTTP daemon; -- or because of the argument to REQUEST or REQUEST_PIECES cannot be -- interpreted as a URL because it is NULL or has non-HTTP syntax) then -- exception UTL_HTTP.REQUEST_FAILED is raised. request_failed exception; -- Note that the above two exceptions, unless explicitly caught by an -- exception handler, will be reported by this generic message: -- ORA-06510: PL/SQL: unhandled user-defined exception -- which reports them as "user-defined" exceptions, although -- they are defined in this system package. -- If any other exception is raised during the processing of the http -- request (for example, an out-of-memory error), then function REQUEST -- or REQUEST_PIECES reraises that exception. -- When no response is received from a request to the given URL -- (for example, because no site corresponding to that URL is contacted) -- then a formatted html error message may be returned. For example: -- -- <HTML> -- <HEAD> -- <TITLE>Error Message</TITLE> -- </HEAD> -- <BODY> -- <H1>Fatal Error 500</H1> -- Can't Access Document: http://home.nothing.comm. -- <P> -- <B>Reason:</B> Can't locate remote host: home.nothing.comm. -- <P> -- -- <P><HR> -- <ADDRESS><A HREF="http://www.w3.org"> -- CERN-HTTPD3.0A</A></ADDRESS> -- </BODY> -- </HTML> -- -- You should not expect for UTL_HTTP.REQUEST or UTL_HTTP.REQUEST_PIECES -- to succeed in contacting a URL unless you can contact that URL by using -- a browser on the same machine (and with the same privileges, environment -- variables, etc.) If REQUEST or REQUEST_PIECES fails (i.e., if it raises -- an exception, or returns a HTML-formatted error message, yet you believe -- that the URL argument is correct), please try contacting that same URL -- with a browser, to verify network availability from your machine. end utl_http;
