CREATE FUNCTION

Purpose

Use the CREATE FUNCTION statement to create a standalone stored function or a call specification. (You can also create a function as part of a package using the CREATE PACKAGE statement.)

A stored function (also called a user function) is a set of PL/SQL statements you can call by name. Stored functions are very similar to procedures, except that a function returns a value to the environment in which it is called. User functions can be used as part of a SQL expression.

A call specification declares a Java method or a third-generation language (3GL) routine so that it can be called from SQL and PL/SQL. The call specification tells Oracle which Java method, or which named function in which shared library, to invoke when a call is made. It also tells Oracle what type conversions to make for the arguments and return value.

Prerequisites

Before a stored function can be created, the user SYS must run a SQL script that is commonly called DBMSSTDX.SQL. The exact name and location of this script depend on your operating system.

To create a function in your own schema, you must have the CREATE PROCEDURE system privilege. To create a function in another user's schema, you must have the CREATE ANY PROCEDURE system privilege. To replace a function in another user's schema, you must have the ALTER ANY PROCEDURE system privilege.

To invoke a call specification, you may need additional privileges (for example, EXECUTE privileges on C library for a C call specification).

To embed a CREATE FUNCTION statement inside an Oracle precompiler program, you must terminate the statement with the keyword END-EXEC followed by the embedded SQL statement terminator for the specific language.

Syntax

create_function::=

Text description of create_function

(invoker_rights_clause::=, parallel_enable_clause::=)

invoker_rights_clause::=

Text description of invoker_rights_clause

parallel_enable_clause::=

Text description of parallel_enable_clause

streaming_clause::=

Text description of streaming_clause

call_spec::=

Text description of call_spec

Java_declaration::=

Text description of Java_declaration

C_declaration::=

Text description of C_declaration

Semantics

OR REPLACE

Specify OR REPLACE to re-create the function if it already exists. Use this clause to change the definition of an existing function without dropping, re-creating, and regranting object privileges previously granted on the function. If you redefine a function, Oracle recompiles it.

Users who had previously been granted privileges on a redefined function can still access the function without being regranted the privileges.

If any function-based indexes depend on the function, Oracle marks the indexes DISABLED.

schema

Specify the schema to contain the function. If you omit schema, Oracle creates the function in your current schema.

function

Specify the name of the function to be created. If creating the function results in compilation errors, Oracle returns an error. You can see the associated compiler error messages with the SHOW ERRORS command.

Restrictions on User-defined Functions

User-defined functions cannot be used in situations that require an unchanging definition. Thus, you cannot use user-defined functions:

• In a CHECK constraint clause of a CREATE TABLE or ALTER TABLE statement
• In a DEFAULT clause of a CREATE TABLE or ALTER TABLE statement

In addition, when a function is called from within a query or DML statement, the function cannot:

• Have OUT or IN OUT parameters
• Commit or roll back the current transaction, create a savepoint or roll back to a savepoint, or alter the session or the system. DDL statements implicitly commit the current transaction, so a user-defined function cannot execute any DDL statements.
• Write to the database, if the function is being called from a SELECT statement. However, a function called from a subquery in a DML statement can write to the database.
• Write to the same table that is being modified by the statement from which the function is called, if the function is called from a DML statement.

Except for the restriction on OUT and IN OUT parameters, Oracle enforces these restrictions not only for the function called directly from the SQL statement, but also for any functions that function calls, and on any functions called from the SQL statements executed by that function or any function it calls.

argument

Specify the name of an argument to the function. If the function does not accept arguments, you can omit the parentheses following the function name.

Restriction on Function Arguments

If you are creating an aggregate function, you can specify only one argument.

IN

Specify IN to indicate that you must supply a value for the argument when calling the function. This is the default.

OUT

Specify OUT to indicate that the function will set the value of the argument.

IN OUT

Specify IN OUT to indicate that a value for the argument can be supplied by you and may be set by the function.

NOCOPY

Specify NOCOPY to instruct Oracle to pass this argument as fast as possible. This clause can significantly enhance performance when passing a large value like a record, an index-by table, or a varray to an OUT or IN OUT parameter. (IN parameter values are always passed NOCOPY.)

• When you specify NOCOPY, assignments made to a package variable may show immediately in this parameter (or assignments made to this parameter may show immediately in a package variable) if the package variable is passed as the actual assignment corresponding to this parameter.
• Similarly, changes made either to this parameter or to another parameter may be visible immediately through both names if the same variable is passed to both.
• If the procedure is exited with an unhandled exception, any assignment made to this parameter may be visible in the caller's variable.

These effects may or may not occur on any particular call. You should use NOCOPY only when these effects would not matter.

RETURN Clause

For datatype, specify the datatype of the function's return value. Because every function must return a value, this clause is required. The return value can have any datatype supported by PL/SQL.

The datatype cannot specify a length, precision, or scale. Oracle derives the length, precision, or scale of the return value from the environment from which the function is called.

If the return type is SYS.AnyDataSet and you intend to use the function in the FROM clause of a query, then you must also specify the PIPELINED clause and define a describe method (ODCITableDescribe) as part of the implementation type of the function.

invoker_rights_clause

The invoker_rights_clause lets you specify whether the function executes with the privileges and in the schema of the user who owns it or with the privileges and in the schema of CURRENT_USER.

This clause also determines how Oracle resolves external names in queries, DML operations, and dynamic SQL statements in the function.

AUTHID Clause

• Specify CURRENT_USER if you want the function to execute with the privileges of CURRENT_USER. This clause creates an invoker-rights function.

  This clause also specifies that external names in queries, DML operations, and dynamic SQL statements resolve in the schema of CURRENT_USER. External names in all other statements resolve in the schema in which the function resides.

• Specify DEFINER if you want the function to execute with the privileges of the owner of the schema in which the function resides, and that external names resolve in the schema where the function resides. This is the default and creates a defined-rights function.

  See Also: Oracle9i Database Concepts and Oracle9i Application Developer's Guide - Fundamentals for information on how CURRENT_USER is determined PL/SQL User's Guide and Reference

DETERMINISTIC Clause

Specify DETERMINISTIC to indicate that the function returns the same result value whenever it is called with the same values for its arguments.

You must specify this keyword if you intend to call the function in the expression of a function-based index or from the query of a materialized view that is marked REFRESH FAST or ENABLE QUERY REWRITE. When Oracle encounters a deterministic function in one of these contexts, it attempts to use previously calculated results when possible rather than re-executing the function.

Do not specify this clause to define a function that uses package variables or that accesses the database in any way that might affect the function's return result. The results of doing so will not be captured if Oracle chooses not to reexecute the function.

The following semantic rules govern the use of the DETERMINISTIC clause:

• You can declare a top-level subprogram DETERMINISTIC.
• You can declare a package-level subprogram DETERMINISTIC in the package specification, but not in the package body.
• You cannot declare DETERMINISTIC a private subprogram (declared inside another subprogram or inside a package body).
• A DETERMINISTIC subprogram can call another subprogram whether the called program is declared DETERMINISTIC or not.

  See Also: Oracle9i Data Warehousing Guide for information on materialized views CREATE INDEX for information on function-based indexes

parallel_enable_clause

PARALLEL_ENABLE is an optimization hint indicating that the function can be executed from a parallel execution server of a parallel query operation. The function should not use session state, such as package variables, as those variables may not be shared among the parallel execution servers.

• The optional PARTITION argument BY clause is used only with functions that have a REF CURSOR argument type. It lets you define the partitioning of the inputs to the function from the REF CURSOR argument.

  Partitioning the inputs to the function affects the way the query is parallelized when the function is used as a table function (that is, in the FROM clause of the query). ANY indicates that the data can be partitioned randomly among the parallel execution servers. Alternatively, you can specify RANGE or HASH partitioning on a specified column list.

• The optional streaming_clause lets you order or cluster the parallel processing by a specified column list.
  • ORDER BY indicates that the rows on a parallel execution server must be locally ordered.
  • CLUSTER BY indicates that the rows on a parallel execution server must have the same key values as specified by the column_list.

The columns specified in all of these optional clauses refer to columns that are returned by the REF CURSOR argument of the function.

PIPELINED Clause

Use PIPELINED to instruct Oracle to return the results of a table function iteratively. A table function returns a collection type (a nested table or varray). You query table functions by using the TABLE keyword before the function name in the FROM clause of the query. For example:

SELECT * FROM TABLE(function_name(...))

Oracle then returns rows as they are produced by the function.

• If you specify the keyword PIPELINED alone (PIPELINED IS ...), the PL/SQL function body should use the PIPE keyword. This keyword instructs Oracle to return single elements of the collection out of the function, instead of returning the whole collection as a single value.
• You can specify PIPELINED USING implementation_type clause if you want to predefine an interface containing the start, fetch, and close operations. The implementation type must implement the ODCITable interface, and must exist at the time the table function is created. This clause is useful for table functions that will be implemented in external languages such as C++ and Java.

  If the return type of the function is SYS.AnyDataSet, then you must also define a describe method (ODCITableDescribe) as part of the implementation type of the function.

  See Also: PL/SQL User's Guide and Reference and Oracle9i Application Developer's Guide - Fundamentals for more information on table functions Oracle9i Data Cartridge Developer's Guide for information on ODCI routines

AGGREGATE USING Clause

Specify AGGREGATE USING to identify this function as an aggregate function, or one that evaluates a group of rows and returns a single row. You can specify aggregate functions in the SELECT list, HAVING clause, and ORDER BY clause.

In the USING clause, specify the name of the implementation type of the function. The implementation type must be an object type containing the implementation of the ODCIAggregate routines. If you do not specify schema, Oracle assumes that the implementation type is in your own schema.

Restriction on Creating Aggregate Functions

If you specify this clause, you can specify only one input argument for the function.

IS | AS Clause

Use the appropriate part of this clause to declare the body of the function.

pl/sql_subprogram_body

Use the pl/sql_subprogram_body to declare the function in a PL/SQL subprogram body.

call_spec

Use the call_spec to map a Java or C method name, parameter types, and return type to their SQL counterparts. In Java_declaration, 'string' identifies the Java implementation of the method.

AS EXTERNAL

AS EXTERNAL is an alternative way of declaring a C method. This clause has been deprecated and is supported for backward compatibility only. Oracle Corporation recommends that you use the AS LANGUAGE C syntax.

Examples

Creating a Function: Examples

The following statement creates the function get_bal on the sample table oe.orders (the PL/SQL is in italics):

CREATE FUNCTION get_bal(acc_no IN NUMBER) 
   RETURN NUMBER 
   IS acc_bal NUMBER(11,2);
 BEGIN 
    SELECT order_total 
    INTO acc_bal 
    FROM orders 
    WHERE customer_id = acc_no; 
    RETURN(acc_bal); 
  END;
/

The get_bal function returns the balance of a specified account.

When you call the function, you must specify the argument acc_no, the number of the account whose balance is sought. The datatype of acc_no is NUMBER.

The function returns the account balance. The RETURN clause of the CREATE FUNCTION statement specifies the datatype of the return value to be NUMBER.

The function uses a SELECT statement to select the balance column from the row identified by the argument acc_no in the orders table. The function uses a RETURN statement to return this value to the environment in which the function is called.

The function created in the preceding example can be used in a SQL statement. For example:

SELECT get_bal(165) FROM DUAL; 

GET_BAL(165)
------------
        2519

The following statement creates PL/SQL standalone function get_val that registers the C routine c_get_val as an external function. (The parameters have been omitted from this example; the PL/SQL is in italics.)

CREATE FUNCTION get_val
   ( x_val IN NUMBER,
    y_val IN NUMBER,
    image IN LONG RAW )
   RETURN BINARY_INTEGER AS LANGUAGE C
     NAME "c_get_val"
    LIBRARY c_utils
    PARAMETERS (...);

Creating Aggregate Functions: Example

The next statement creates an aggregate function called SecondMax to aggregate over number values. It assumes that the object type SecondMaxImpl routines contains the implementations of the ODCIAggregate routines:

CREATE FUNCTION SecondMax (input NUMBER) RETURN NUMBER
    PARALLEL_ENABLE AGGREGATE USING SecondMaxImpl;

You would use such an aggregate function in a query like the following statement, which queries the sample table hr.employees:

SELECT SecondMax(salary), department_id
      FROM employees
      GROUP BY department_id
      HAVING SecondMax(salary) > 9000;

SECONDMAX(SALARY) DEPARTMENT_ID
----------------- -------------
            13500            80
            17000            90

Using a Packaged Procedure in a Function: Example

The following statement creates a function that uses a DBMS_LOB procedure to return the length of a CLOB column:

CREATE OR REPLACE FUNCTION text_length(a CLOB) 
   RETURN NUMBER DETERMINISTIC IS
BEGIN 
  RETURN DBMS_LOB.GETLENGTH(a);
END;