創建UDF:

　　CREATE [AGGREGATE] FUNCTION function_name(parameter_name type,[parameter_name type,...])
　　RETURNS {STRING|INTEGER|REAL}
　　runtime_body

刪除UDF:

調用自定義函數語法:

例子1

CREATE FUNCTION simpleFun() RETURNS VARCHAR(20)
BEGIN
  RETURN "Hello World!";
end;

select simpleFun();

例子2

CREATE TABLE son (
  id INT NOT NULL
 
,
  name VARCHAR(20),
  pay INTEGER
);
INSERT INTO son (id, name, pay) VALUES (1,‘bol‘,20);
INSERT INTO son (id, name, pay) VALUES (2,‘davie‘,2220);
SELECT * FROM son;
DROP FUNCTION IF EXISTS deleteById;
CREATE FUNCTION deleteById(uid SMALLINT UNSIGNED)
RETURNS VARCHAR(20)
BEGIN
DELETE FROM son WHERE id = uid;
RETURN 
 
(SELECT COUNT(id) FROM son);
END
select deleteById(2);

DELIMITER $$
DROP FUNCTION IF EXISTS `test`;
CREATE FUNCTION `test`(gdate datetime) RETURNS varchar(255)
BEGIN
DECLARE x VARCHAR(255) DEFAULT ‘‘;
SET x= date_format(gdate,‘%Y%m%d%h%i%s‘);
RETURN x;
END $$
DELIMITER ;
SELECT test(‘2009-06-23 00:00:00‘)

DELIMITER $$
DROP FUNCTION IF EXISTS cutString ;
CREATE FUNCTION cutString(s VARCHAR(255),n INT) RETURNS varchar(255)
BEGIN
   IF(ISNULL(s)) THEN RETURN ‘‘;
   ELSEIF CHAR_LENGTH(s)<n THEN 
            RETURN s;
   ELSEIF CHAR_LENGTH(S)=n THEN 
            RETURN ‘相等‘;
   ELSE 
            RETURN CONCAT(LEFT(s,n),‘...‘);
   END IF;
END $$
DELIMITER ;
SELECT cutString(‘323432234‘,4);