Oracle7 Server SQL Reference

User Functions

You can write your own user functions in PL/SQL to provide functionality that is not available in SQL or SQL functions. User functions are used in a SQL statement anywhere SQL functions can be used; that is, wherever expression can occur.

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

the select list of a SELECT command

the condition of a WHERE clause

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

the VALUES clause of an INSERT command

the SET clause of an UPDATE command

For a complete description on the creation and usage of user functions, see Oracle7 Server Application Developer's Guide.

Prequisites

User functions must be created as top-level PL/SQL functions or declared with a package specification before they can be named within a SQL statement. User functions are created as top-level PL/SQL functions by using the CREATE FUNCTION statement described

. Packaged functions are specified with a package with the CREATE PACKAGE statement described

To call a packaged user function, you must declare the RESTRICT_REFERENCES pragma in the package specification.

Privileges Required

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.

Restrictions on User Functions

User functions cannot be used in situations that require an unchanging definition. Thus, a user function:

cannot be used in a CHECK constraint clause of a CREATE TABLE or ALTER TABLE command

cannot be used in a DEFAULT clause of a CREATE TABLE or ALTER TABLE command

cannot contain OUT or IN OUT parameters

cannot update the database

cannot read or write package state if the function is a remote function

cannot use the parallelism_clause in SQL commands in the function if the function alters package state

cannot update variables defined in the function unless the function is a local function and is used in a SELECT list, VALUES clause of an INSERT command, or SET clause of an UPDATE command

Name Precedence

With PL/SQL, 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 ,,,;

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;

Example I

For 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;

Example II

Listed below are 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

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:

check for the PAYROLL package in the current schema

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, an error message is returned

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, an error message is returned

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