User-Defined Functions

Feature compatibility	AWS SCT / AWS DMS automation level	AWS SCT action code index	Key differences
		Stored Procedures	Syntax and option differences.

Oracle Usage

You can create an Oracle user-defined function (UDF) using PL/SQL, Java, or C. UDFs are useful for providing functionality not available in SQL or SQL built-in functions. They can appear in SQL statements wherever built-in SQL functions can appear.

You can use UDFs in the following cases:

• To return a single value from a SELECT statement (scalar function).

• While performing DML operations.

• In WHERE, GROUP BY, ORDER BY, HAVING, CONNECT BY, and START WITH clauses.

Examples

Create a simple Oracle UDF with arguments for employee HIRE_DATE and SALARY as INPUT parameters and calculate the overall salary over the employee’s years of service for the company.

CREATE OR REPLACE FUNCTION TOTAL_EMP_SAL_BY_YEARS
(p_hire_date DATE, p_current_sal NUMBER)
RETURN NUMBER
AS
v_years_of_service NUMBER;
v_total_sal_by_years NUMBER;
BEGIN
SELECT EXTRACT(YEAR FROM SYSDATE) - EXTRACT(YEAR FROM to_date(p_hire_date))
INTO v_years_of_service FROM dual;
v_total_sal_by_years:=p_current_sal*v_years_of_service;
RETURN v_total_sal_by_years;
END;
/
-- Verifying
SELECT EMPLOYEE_ID, FIRST_NAME, TOTAL_EMP_SAL_BY_YEARS(HIRE_DATE, SALARY)AS TOTAL_
SALARY
FROM EMPLOYEES;

EMPLOYEE_ID FIRST_NAME TOTAL_SALARY
100         Steven     364000
101         Neena      204000
102         Lex        272000
103         Alexander  99000
104         Bruce      60000
105         David      57600
…

For more information, see CREATE FUNCTION in the Oracle documentation.

PostgreSQL Usage

PostgreSQL supports the creation of user-defined functions using the CREATE FUNCTION statement. The PostgreSQL extended SQL language, PL/pgSQL, is the primary language to use while migrating from Oracle PL/SQL user-defined functions.

To create a function, a user needs the USAGE privilege on the language.

Examples

Convert the Oracle user-defined function from the previous Oracle section to a PostgreSQL PL/pgSQL function.

CREATE OR REPLACE FUNCTION total_emp_sal_by_years
(P_HIRE_DATE DATE, P_CURRENT_SAL NUMERIC)
RETURNS NUMERIC
AS
$BODY$
DECLARE
V_YEARS_OF_SERVICE NUMERIC;
V_TOTAL_SAL_BY_YEARS NUMERIC;
BEGIN
SELECT EXTRACT(YEAR FROM NOW()) - EXTRACT(YEAR FROM (P_HIRE_DATE)) INTO V_YEARS_OF_SERVICE;
V_TOTAL_SAL_BY_YEARS:=P_CURRENT_SAL*V_YEARS_OF_SERVICE;
RETURN V_TOTAL_SAL_BY_YEARS;
END;
$BODY$
LANGUAGE PLPGSQL;

SELECT EMPLOYEE_ID, FIRST_NAME, TOTAL_EMP_SAL_BY_YEARS(HIRE_DATE, SALARY)AS TOTAL_SALARY
FROM EMPLOYEES;

employee_id  first_name  total_salary
100          Steven      364000.00
101          Neena       204000.00
102          Lex         272000.00
103          Alexander   99000.00
104          Bruce       60000.00
105          David       57600.00
106          Valli       52800.00
107          Diana       42000.00
…

For more information, see User-Defined Functions and CREATE FUNCTION in the PostgreSQL documentation, and What is the AWS Schema Conversion Tool? in the user guide.