You can use any built-in SQL function or user-defined function as an expression. Some valid built-in function expressions are:
LENGTH('BLAKE')
ROUND(1234.567*43)
SYSDATE
A user-defined function expression specifies a call to:
A function in an Oracle-supplied package (see Oracle Database PL/SQL Packages and Types Reference)
A function in a user-defined package or type or in a standalone user-defined function (see "About User-Defined Functions")
A user-defined function or operator (see CREATE OPERATOR, CREATE FUNCTION, and Oracle Database Data Cartridge Developer's Guide)
Some valid user-defined function expressions are:
circle_area(radius) payroll.tax_rate(empno) hr.employees.comm_pct@remote(dependents, empno) DBMS_LOB.getlength(column_name) my_function(a_column)
In a user-defined function being used as an expression, positional, named, and mixed notation are supported. For example, all of the following notations are correct:
CALL my_function(arg1 => 3, arg2 => 4) ...
CALL my_function(3, 4) ... CALL my_function(3, arg2 => 4) ...
Restriction on User-Defined Function Expressions You cannot pass arguments of object type or XMLType to remote functions and procedures.