You can write user-defined functions in PL/SQL, Java, or C to provide functionality that is not available in SQL or SQL built-in functions. User-defined functions can appear in a SQL statement wherever an expression can occur.
For example, user-defined functions can be used in the following:
The select list of a
The condition of a
VALUES clause of an
SET clause of an
Note:Oracle SQL does not support calling of functions with Boolean parameters or returns. Therefore, if your user-defined functions will be called from SQL statements, you must design them to return numbers (0 or 1) or character strings ('
TRUE' or '
The optional expression list must match attributes of the function, package, or operator.
User-defined functions must be created as top-level functions or declared with a package specification before they can be named within a SQL statement.
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 the
SELECT privilege on the view. No separate
EXECUTE privileges are needed to select from the view.
Within a SQL statement, the names of database columns take precedence over the names of functions with no parameters. For example, if the Human Resources manager creates the following two objects in the
CREATE TABLE new_emps (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
SELECT new_sal FROM new_emps; SELECT new_emps.new_sal FROM new_emps;
To access the function
new_sal, you would enter:
SELECT hr.new_sal FROM new_emps;
Here are some sample calls to user functions that are allowed in SQL expressions:
circle_area (radius) payroll.tax_rate (empno) hr.employees.tax_rate (dependent, empno)@remote
SELECT hr.tax_rate (ss_no, sal) INTO income_tax FROM tax_table WHERE ss_no = tax_id;
INTO clause is PL/SQL that lets you place the results into the variable
If only one of the optional schema or package names is given, then the first identifier can be either a schema name or a package name. For example, to determine whether
PAYROLL in the reference
TAX_RATE is a schema or package name, Oracle Database proceeds as follows:
Check for the
PAYROLL package in the current schema.
PAYROLL package is not found, then look for a schema name
PAYROLL that contains a top-level
TAX_RATE function. If no such function is found, then return an error.
PAYROLL package is found in the current schema, then look for a
TAX_RATE function in the
PAYROLL package. If no such function is found, then return an error.
You can also refer to a stored top-level function using any synonym that you have defined for it.