MySQL自定义函数与存储过程

1、前置条件

MySQL数据库中存在表user_info，其结构和数据如下：

mysql> desc  user_info;
+-----------+----------+------+-----+---------+-------+
| Field     | Type     | Null | Key | Default | Extra |
+-----------+----------+------+-----+---------+-------+
| id        | int(10)  | NO   | PRI | NULL    |       |
| name      | char(20) | NO   |     | NULL    |       |
| passwd    | char(40) | NO   |     | NULL    |       |
| email     | char(20) | NO   |     | NULL    |       |
| phone     | char(20) | NO   |     | NULL    |       |
| role      | char(10) | NO   |     | NULL    |       |
| sex       | char(10) | NO   |     | NULL    |       |
| status    | int(10)  | NO   |     | NULL    |       |
| createAt  | datetime | NO   |     | NULL    |       |
| exprAt    | datetime | NO   |     | NULL    |       |
| validDays | int(10)  | NO   |     | NULL    |       |
| delAt     | datetime | YES  |     | NULL    |       |
+-----------+----------+------+-----+---------+-------+
12 rows in set (0.10 sec)

mysql> select  * from  user_info;
+----+--------------+----------+------------+-------------+--------+------+--------+---------------------+---------------------+-----------+-------+
| id | name         | passwd   | email      | phone       | role   | sex  | status | createAt            | exprAt              | validDays | delAt |
+----+--------------+----------+------------+-------------+--------+------+--------+---------------------+---------------------+-----------+-------+
|  1 | StephenWang7 | py123456 | 123@qq.com | 15103887470 | admin  | male |    200 | 2019-04-12 20:11:30 | 2019-04-19 20:11:30 |        30 | NULL  |
|  2 | StephenWang8 | 123456   | 123@qq.com | 15103887470 | viewer | male |    200 | 2019-04-12 20:11:30 | 2019-04-19 20:11:30 |        30 | NULL  |
+----+--------------+----------+------------+-------------+--------+------+--------+---------------------+---------------------+-----------+-------+
2 rows in set (0.00 sec)

2、自定义函数

函数：可以完成特定功能的一段SQL集合。MySQL支持自定义函数来完成特定的业务功能。
创建自定义函数（User Defined Function 简称UDF）的语法如下：

create function <函数名称> （[参数1] [类型1], [参数N] [类型N]）
returns <类型>
return 
<函数主体>

调用UDF的语法如下：

创建无参的UDF

示例1：查询user_info表中有多少条记录

#定义函数
mysql> create function  user_info_count()
    -> returns int(10)
    -> return
    -> (select  count(*) from user_info);

调用函数user_info_count()

mysql> select  user_info_count();
+-------------------+
| user_info_count() |
+-------------------+
|                 2 |
+-------------------+
1 row in set (0.00 sec)

创建有参UDF

示例2：根据id查询用户name。

#定义函数
mysql> create function  queryNameById(uid int(10))
    -> returns char(20)
    -> return
    -> (select  name  from   user_info  where id=uid);
Query OK, 0 rows affected (0.01 sec)

调用函数，查询id为1的用户名称。

mysql> select  queryNameById(1);
+------------------+
| queryNameById(1) |
+------------------+
| StephenWang7     |
+------------------+
1 row in set (0.00 sec)

查看UDF

查询系统中所有的UDF

show function status;

查询指定的UDF

#
show   create function   函数名称;
mysql> show  function   queryNameById;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'queryNameById' at line 1
mysql> show  function   queryNameById();
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'queryNameById()' at line 1
mysql> show   create function   queryNameById();
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '()' at line 1
mysql> show   create function   queryNameById;
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| Function      | sql_mode                                                                                                                                  | Create Function                                                                                                                                               | character_set_client | collation_connection | Database Collation |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| queryNameById | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | CREATE DEFINER=`root`@`localhost` FUNCTION `queryNameById`(uid int(10)) RETURNS char(20) CHARSET latin1
return (select  name  from   user_info  where id=uid) | utf8                 | utf8_general_ci      | latin1_swedish_ci  |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec

修改UDF

如果想要修改函数的内容，先删除后再重新创建。

删除UDF

删除UDF语法如下：

drop function  <函数名称>;

示例3：删除函数queryNameId后再次调用并观察现象。

mysql> drop  function queryNameById;
Query OK, 0 rows affected (0.45 sec)

mysql> select queryNameById(1);
ERROR 1305 (42000): FUNCTION rms.queryNameById does not exist
mysql> 

3、存储过程

存储功能和自定义函数相似，也是一组完成特定功能的SQL语句集合。把复杂或频繁调用的SQL提前写好并指定一个名称。待到要使用时，直接调用即可。
定义存储过程的语法如下：

CREATE PROCEDURE <过程名> ( [过程参数[,…] ] ) <过程体>
[过程参数[,…] ] 格式
[ IN | OUT | INOUT ] <参数名> <类型>
#语法定义来自：http://c.biancheng.net/view/2593.html

创建无参的存储过程

示例4：查询用户name。

mysql> DELIMITER //
mysql> craete procedure queryName()
    -> begin
    -> select  name from user_info;
    -> end //

关于DELIMITER命令，修改MySQL结束命令的字符。默认的结束命令字符为分号，当存储过程中包含多条语句时，遇到第一个分号会作为存储过程结束的标志。这样不符合预期，因此需要修改默认结束命令字符。 DELIMITER //就是将结束命令字符修改为//。调用存储过程的命令为：call 存储过程名称。

#此时的命令的结束符号为// 不是;
mysql> call  queryName()//
+--------------+
| name         |
+--------------+
| StephenWang7 |
| StephenWang8 |
+--------------+
2 rows in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

创建带参数的存储过程

示例5：根据id查询name。

mysql> create procedure  queryNameById
    -> (In uid int(15))
    -> begin
    -> select  name  from  user_info where id=uid;
    -> end
    -> //
Query OK, 0 rows affected (0.03 sec)

调用存储过程queryNameById

mysql> call queryNameById(1);
    -> //
+--------------+
| name         |
+--------------+
| StephenWang7 |
+--------------+
1 row in set (0.03 sec)

Query OK, 0 rows affected (0.04 sec)

修改存储过程

如果想创建存储过程的内容可以先删除再重新创建存储过程。

查看存储过程

show create procedure <过程名称>

    -> //
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| Procedure     | sql_mode                                                                                                                                  | Create Procedure                                                                                                                  | character_set_client | collation_connection | Database Collation |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| queryNameById | ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION | CREATE DEFINER=`root`@`localhost` PROCEDURE `queryNameById`(In uid int(15))
begin
select  name  from  user_info where id=uid;
end | utf8                 | utf8_general_ci      | latin1_swedish_ci  |
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
1 row in set (0.04 sec)

删除存储过程

drop procedure <过程名称>

删除存储过程queryNameById

mysql> drop procedure  queryNameById//
Query OK, 0 rows affected (0.02 sec)


mysql> call  queryNameById(1)//
ERROR 1305 (42000): PROCEDURE rms.queryNameById does not exist

4、总结

自定义函数和存储过程都是完成特定功能的SQL集合，那么他们有什么不同呢？
a、调用方式不同

#自定义函数
select  <函数名>
#存储过程
call <存储过程名>

b、自定义函数不能有输出参数，而存储过程可以。
c、自定义函数必须要包含return语句，而存储过程则不需要。