什么是MySQL自定義函數(shù)與創(chuàng)建存儲過程

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1、前置條件

MySQL數(shù)據(jù)庫中存在表user_info，其結(jié)構(gòu)和數(shù)據(jù)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、自定義函數(shù)

函數(shù)：可以完成特定功能的一段SQL集合。MySQL支持自定義函數(shù)來完成特定的業(yè)務功能。
創(chuàng)建自定義函數(shù)（User Defined Function 簡稱UDF）的語法如下：

create function <函數(shù)名稱> （[參數(shù)1] [類型1], [參數(shù)N] [類型N]）
returns <類型>
return 
<函數(shù)主體>

調(diào)用UDF的語法如下：

select  <函數(shù)名稱> ([參數(shù)])

創(chuàng)建無參的UDF

示例1：查詢user_info表中有多少條記錄

#定義函數(shù)
mysql> create function  user_info_count()
    -> returns int(10)
    -> return
    -> (select  count(*) from user_info);

調(diào)用函數(shù)user_info_count()

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

創(chuàng)建有參UDF

示例2：根據(jù)id查詢用戶name。

#定義函數(shù)
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)

調(diào)用函數(shù)，查詢id為1的用戶名稱。

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

查看UDF

查詢系統(tǒng)中所有的UDF

show function status;

查詢指定的UDF

#
show   create function   函數(shù)名稱;
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

如果想要修改函數(shù)的內(nèi)容，先刪除后再重新創(chuàng)建。

刪除UDF

刪除UDF語法如下：

drop function  <函數(shù)名稱>;

示例3：刪除函數(shù)queryNameId后再次調(diào)用并觀察現(xiàn)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、存儲過程

存儲功能和自定義函數(shù)相似，也是一組完成特定功能的SQL語句集合。把復雜或頻繁調(diào)用的SQL提前寫好并指定一個名稱。待到要使用時，直接調(diào)用即可。
定義存儲過程的語法如下：

CREATE PROCEDURE <過程名> ( [過程參數(shù)[,…] ] ) <過程體>
[過程參數(shù)[,…] ] 格式
[ IN | OUT | INOUT ] <參數(shù)名> <類型>
#語法定義來自：http://c.biancheng.net/view/2593.html

創(chuàng)建無參的存儲過程

示例4：查詢用戶name。

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

關(guān)于DELIMITER命令，修改MySQL結(jié)束命令的字符。默認的結(jié)束命令字符為分號，當存儲過程中包含多條語句時，遇到第一個分號會作為存儲過程結(jié)束的標志。這樣不符合預期，因此需要修改默認結(jié)束命令字符。 DELIMITER //就是將結(jié)束命令字符修改為//。調(diào)用存儲過程的命令為：call 存儲過程名稱。

#此時的命令的結(jié)束符號為// 不是;
mysql> call  queryName()//
+--------------+
| name         |
+--------------+
| StephenWang7 |
| StephenWang8 |
+--------------+
2 rows in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

創(chuàng)建帶參數(shù)的存儲過程

示例5：根據(jù)id查詢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)

調(diào)用存儲過程queryNameById

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

Query OK, 0 rows affected (0.04 sec)

修改存儲過程

如果想創(chuàng)建存儲過程的內(nèi)容可以先刪除再重新創(chuàng)建存儲過程。

查看存儲過程

show create procedure <過程名稱>

mysql> show create procedure queryNameById; -> // +---------------+-------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+ | 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)

刪除存儲過程

drop procedure <過程名稱>

刪除存儲過程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、總結(jié)

自定義函數(shù)和存儲過程都是完成特定功能的SQL集合，那么他們有什么不同呢？
a、調(diào)用方式不同

#自定義函數(shù)
select  <函數(shù)名>
#存儲過程
call <存儲過程名>

b、自定義函數(shù)不能有輸出參數(shù)，而存儲過程可以。
c、自定義函數(shù)必須要包含return語句，而存儲過程則不需要。

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