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
VALUESclause of an
SETclause of an
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.
Restriction on User-defined Functions
ALL keywords are valid only with a user-defined aggregate function.
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
To call the
tax_rate user function from schema
hr, execute it against the
sal columns in
tax_table, specify the following:
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
PAYROLLpackage in the current schema.
PAYROLLpackage is not found, then look for a schema name
PAYROLLthat contains a top-level
TAX_RATEfunction. If no such function is found, then return an error.
PAYROLLpackage is found in the current schema, then look for a
TAX_RATEfunction in the
PAYROLLpackage. 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.