mysql自定义函数

一、自定义函数（UDF）的特性和功能  www.2cto.com 
        函数能分返回字符串，整数或实数;
        可以定义一次作用于一行的简单函数，或作用于多行的组的集合函数;
二、基本操作
1、创建自定义函数
        CREATE [AGGREGATE] FUNCTION function_name RETURNS {STRING|INTEGER|REAL}
        BEGIN
            //函数实现的语句
        END;
        aggregate 指定创建的函数是普通的自定义函数，还是AGGREGATE函数。
        function_name 是用在SQL声明中以备调用的函数名字。
        RETURNS 子句说明函数返回值的类型。
        每次服务器启动的时候会重新加载所有有效函数，除非使用--skip-grant-tables参数启动mysqld。在这种情况下， 将跳过UDF的初始化，UDF不可用。
        一个AGGREGATE函数就像一个MySQL固有的集合（总和）函数一样起作用，比如，SUM或COUNT()函数。要使得AGGREGATE 起作用，mysql.func表必须包括一个type列。如果mysql.func表没有这一 列，则应该运行mysql_fix_privilege_tables脚本来创建此列。
        示例：
[sql]
mysql> delimiter // 
mysql> create function fun_add_rand( 
    ->     in_int int 
    -> ) 
    -> RETURNS int 
    -> BEGIN 
    ->     declare i_rand int; 
    ->     declare i_return int; 
    -> 
    ->     set i_rand=floor(rand()*100); 
    ->     set i_return = in_int + i_rand; 
    -> 
    ->     return i_return; 
    -> END; 
    -> // 
mysql> delimiter ; 

2、使用自定义函数
        示例：
[sql]
mysql> select id from test_inn; 
+------+ 
| id   | 
+------+ 
|    1 | 
|    1 | 
|    1 | 
|    1 | 
+------+ 
mysql> select fun_add_rand(id) from test_inn; 
+------------------+ 
| fun_add_rand(id) | 
+------------------+ 
|               91 | 
|               34 | 
|               93 | 
|               66 | 
+------------------+ 

3、删除自定义函数
        DROP FUNCTION [ IF EXISTS ] function_name;
        示例：
[sql]
mysql> drop function if exists fun_add_rand; 

4、查看自定义函数创建信息
        SHOW CREATE FUNTION function_name;
        示例：
[sql]
mysql> show create function fun_add_rand;                                                                                                                  
+--------------+----------+-----------------------------------------------------------+----------------------+----------------------+--------------------+ 
| Function     | sql_mode | Create Function                                           | character_set_client | collation_connection | Database Collation | 
+--------------+----------+-----------------------------------------------------------+----------------------+----------------------+--------------------+ 
| fun_add_rand |          | CREATE DEFINER=`root`@`localhost` FUNCTION `fun_add_rand`(                                                                     
    in_int int                                                                     
) RETURNS int(11)                                                                     
BEGIN                                                                     
    declare i_rand int;                                                                     
    declare i_return int;                                                                     
                                                                     
    set i_rand=floor(rand()*100);                                                                     
    set i_return = in_int + i_rand;                                                                     
                                                                     
    return i_return;                                                                     
END | latin1               | latin1_swedish_ci    | latin1_swedish_ci  |                                                                     
+--------------+----------+-----------------------------------------------------------+----------------------+----------------------+--------------------+ 

5、查看自定义函数状态
        SHOW FUNCTION STATUS [ LIKE '' ];
        示例：
[sql]
mysql> show function status like 'fun%'; 
+------+--------------+----------+----------------+---------------------+---------------------+---------------+ 
| Db   | Name         | Type     | Definer        | Modified            | Created             | Security_type | 
+------+--------------+----------+----------------+---------------------+---------------------+---------------+ 
| test | fun_add_rand | FUNCTION | root@localhost | 2012-12-18 20:08:50 | 2012-12-18 20:08:50 | DEFINER       | 
+------+--------------+----------+----------------+---------------------+---------------------+---------------+