CREATE FUNCTION function_name
RETURNS
{STRING|INTEGER|REAL|DECIMAL}
routine_body

mysql> CREATE FUNCTION f1() RETURNS VARCHAR(30)                 
    -> RETURN DATE_FORMAT(NOW(),‘%Y年%m月%d日 %H點:%i分:%s秒‘); 
Query OK, 0 rows affected (0.00 sec)
 
mysql> SELECT f1();
+-------------------------------------+
| f1()                                |
 

+-------------------------------------+
| 2016年11月28日 08點:34分:55秒       |
+-------------------------------------+

mysql> CREATE FUNCTION f2(num1 SMALLINT UNSIGNED,num2 SMALLINT UNSIGNED)
    -> RETURNS FLOAT(10,2) UNSIGNED
    -> RETURN (num1+num2)/2;
Query OK, 
 
0 rows affected (0.00 sec)
 
mysql> SELECT f2(10,16);
+-----------+
| f2(10,16) |
+-----------+
|     13.00 |
+-----------+

DROP FUNCTION [IF EXISTS] function_name

mysql> DELIMITER //
mysql> CREATE FUNCTION adduser(username VARCHAR(20))
    -> RETURNS INT UNSIGNED
    -> BEGIN
    -> INSERT test(username) VALUES(username);
    -> RETURN LAST_INSERT_ID();
    -> END
    -> //  
mysql> DELIMITER ;
mysql> SELECT adduser(‘Tom‘);
+----------------+
| adduser(‘Tom‘) |
+----------------+
|              3 |
+----------------+
 
mysql> SELECT adduser(‘Rool‘);
+-----------------+
| adduser(‘Rool‘) |
+-----------------+
|               4 |
+-----------------+
 
mysql> SELECT * FROM user;
+----+----------+
| id | username |
+----+----------+
|  1 | Drive    |
|  2 | Cve      |
|  3 | Tom      |
|  4 | Rool     |
+----+----------+

MySQL學習筆記-自定義函數