User-Defined Functions

You can write user-defined functions in PL/SQL or Java to provide functionality that is not available in SQL or SQL functions. User functions can appear in a SQL statement anywhere SQL functions can appear, that is, wherever an expression can occur.

For example, user functions can be used in the following:

• The select list of a SELECT statement

• The condition of a WHERE clause

• CONNECT BY, START WITH, ORDER BY, and GROUP BY clauses

• The VALUES clause of an INSERT statement

• The SET clause of an UPDATE statement

  See Also: "CREATE FUNCTION" for information on creating functions, including restrictions on user-defined functions. Oracle8i Application Developer's Guide - Fundamentals for a complete description on the creation and use of user functions.

Prerequisites

User functions must be created as top-level functions or declared with a package specification before they can be named within a SQL statement. Create user functions as top-level functions by using the CREATE FUNCTION statement described in "CREATE FUNCTION". To specify packaged functions, see "CREATE PACKAGE".

To use a user function in a SQL expression, you must own or have EXECUTE privilege on the user function. To query a view defined with a user function, you must have SELECT privileges on the view. No separate EXECUTE privileges are needed to select from the view.

Name Precedence

Within a SQL statement, the names of database columns take precedence over the names of functions with no parameters. For example, if user SCOTT creates the following two objects in his own schema:

CREATE TABLE emp(new_sal NUMBER, ...);
CREATE FUNCTION new_sal RETURN NUMBER IS BEGIN ... END;

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:

SELECT scott.new_sal FROM emp;

Here are some sample calls to user functions that are allowed in SQL expressions:

circle_area (radius)
payroll.tax_rate (empno)
scott.payroll.tax_rate (dependent, empno)@ny

Example

To call the TAX_RATE user 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;

Naming Conventions

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:

1. Check for the PAYROLL package in the current schema.

2. If a PAYROLL package is not found, look for a schema name PAYROLL that contains a top-level TAX_RATE function. If no such function is found, return an error.

3. If the PAYROLL package is found in the current schema, look for a TAX_RATE function in the PAYROLL package. If no such function is found, return an error.

You can also refer to a stored top-level function using any synonym that you have defined for it.