---------------------------------------------------------------------------
--
-- funcs.sql-
-- Tutorial on using functions in POSTGRES.
--
--
-- Copyright (c) 1994-5, Regents of the University of California
--
-- src/tutorial/funcs.source
--
---------------------------------------------------------------------------
-----------------------------
-- Creating SQL Functions on Base Types
-- a CREATE FUNCTION statement lets you create a new function that
-- can be used in expressions (in SELECT, INSERT, etc.). We will start
-- with functions that return values of base types.
-----------------------------
--
-- let's create a simple SQL function that takes no arguments and
-- returns 1
CREATE FUNCTION one() RETURNS integer
AS 'SELECT 1 as ONE' LANGUAGE SQL;
--
-- functions can be used in any expressions (eg. in the target list or
-- qualifications)
SELECT one() AS answer;
--
-- here's how you create a function that takes arguments. The following
-- function returns the sum of its two arguments:
CREATE FUNCTION add_em(integer, integer) RETURNS integer
AS 'SELECT $1 + $2' LANGUAGE SQL;
SELECT add_em(1, 2) AS answer;
-----------------------------
-- Creating SQL Functions on Composite Types
-- it is also possible to create functions that return values of
-- composite types.
-----------------------------
-- before we create more sophisticated functions, let's populate an EMP
-- table
CREATE TABLE EMP (
name text,
salary integer,
age integer,
cubicle point
);
INSERT INTO EMP VALUES ('Sam', 1200, 16, '(1,1)');
INSERT INTO EMP VALUES ('Claire', 5000, 32, '(1,2)');
INSERT INTO EMP VALUES ('Andy', -1000, 2, '(1,3)');
INSERT INTO EMP VALUES ('Bill', 4200, 36, '(2,1)');
INSERT INTO EMP VALUES ('Ginger', 4800, 30, '(2,4)');
-- the argument of a function can also be a tuple. For instance,
-- double_salary takes a tuple of the EMP table
CREATE FUNCTION double_salary(EMP) RETURNS integer
AS 'SELECT $1.salary * 2 AS salary' LANGUAGE SQL;
SELECT name, double_salary(EMP) AS dream
FROM EMP
WHERE EMP.cubicle ~= '(2,1)'::point;
-- the return value of a function can also be a tuple. However, make sure
-- that the expressions in the target list is in the same order as the
-- columns of EMP.
CREATE FUNCTION new_emp() RETURNS EMP
AS 'SELECT ''None''::text AS name,
1000 AS salary,
25 AS age,
''(2,2)''::point AS cubicle'
LANGUAGE SQL;
-- you can then project a column out of resulting the tuple by using the
-- "function notation" for projection columns. (ie. bar(foo) is equivalent
-- to foo.bar) Note that we don't support new_emp().name at this moment.
SELECT name(new_emp()) AS nobody;
-- let's try one more function that returns tuples
CREATE FUNCTION high_pay() RETURNS setof EMP
AS 'SELECT * FROM EMP where salary > 1500'
LANGUAGE SQL;
SELECT name(high_pay()) AS overpaid;
-----------------------------
-- Creating SQL Functions with multiple SQL statements
-- you can also create functions that do more than just a SELECT.
-----------------------------
-- you may have noticed that Andy has a negative salary. We'll create a
-- function that removes employees with negative salaries.
SELECT * FROM EMP;
CREATE FUNCTION clean_EMP () RETURNS integer
AS 'DELETE FROM EMP WHERE EMP.salary <= 0;
SELECT 1 AS ignore_this'
LANGUAGE SQL;
SELECT clean_EMP();
SELECT * FROM EMP;
-----------------------------
-- Creating C Functions
-- in addition to SQL functions, you can also create C functions.
-- See funcs.c for the definition of the C functions.
-----------------------------
CREATE FUNCTION add_one(integer) RETURNS integer
AS '_OBJWD_/funcs' LANGUAGE C;
CREATE FUNCTION makepoint(point, point) RETURNS point
AS '_OBJWD_/funcs' LANGUAGE C;
CREATE FUNCTION copytext(text) RETURNS text
AS '_OBJWD_/funcs' LANGUAGE C;
CREATE FUNCTION c_overpaid(EMP, integer) RETURNS boolean
AS '_OBJWD_/funcs' LANGUAGE C;
SELECT add_one(3) AS four;
SELECT makepoint('(1,2)'::point, '(3,4)'::point ) AS newpoint;
SELECT copytext('hello world!');
SELECT name, c_overpaid(EMP, 1500) AS overpaid
FROM EMP
WHERE name = 'Bill' or name = 'Sam';
-- remove functions that were created in this file
DROP FUNCTION c_overpaid(EMP, integer);
DROP FUNCTION copytext(text);
DROP FUNCTION makepoint(point, point);
DROP FUNCTION add_one(integer);
--DROP FUNCTION clean_EMP();
DROP FUNCTION high_pay();
DROP FUNCTION new_emp();
DROP FUNCTION add_em(integer, integer);
DROP FUNCTION one();
DROP FUNCTION double_salary(EMP);
DROP TABLE EMP;
Generated by dwww version 1.15 on Sat May 18 11:56:38 CEST 2024.