1、前置條件
MySQL數據庫中存在表user_info，其結構和數據如下：
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
函數：可以完成特定功能的一段SQL集合。MySQL支持自定義函數來完成特定的業務功能。
創建自定義函數（User Defined Function 簡稱UDF）的語法如下：
create function <函數名稱> （[參數1] [類型1], [參數N] [類型N]）
returns <類型>
return
<函數主體>
調用UDF的語法如下：
創建無參的UDF
示例1：查詢user_info表中有多少條記錄
#定義函數
mysql> create function user_info_count()
-> returns int(10)
-> return
-> (select count(*) from user_info);
調用函數user_info_count()
mysql> select user_info_count();
+-------------------+
| user_info_count() |
+-------------------+
| 2 |
+-------------------+
1 row in set (0.00 sec)
創建有參UDF
示例2：根據id查詢用戶name。
#定義函數
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)
調用函數，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
查詢系統中所有的UDF
show function status;
查詢指定的UDF
#
show create function 函數名稱;
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
如果想要修改函數的內容，先刪除后再重新創建。
刪除UDF
刪除UDF語法如下：
drop function <函數名稱>;
示例3：刪除函數queryNameId后再次調用並觀察現象。
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。把復雜或頻繁調用的SQL提前寫好並指定一個名稱。待到要使用時，直接調用即可。
定義存儲過程的語法如下：
CREATE PROCEDURE <過程名> ( [過程參數[,…] ] ) <過程體>
[過程參數[,…] ] 格式
[ IN | OUT | INOUT ] <參數名> <類型>
#語法定義來自：http://c.biancheng.net/view/2593.html
創建無參的存儲過程
示例4：查詢用戶name。
mysql> DELIMITER //
mysql> craete procedure queryName()
-> begin
-> select name from user_info;
-> end //
關於DELIMITER命令，修改MySQL結束命令的字符。默認的結束命令字符為分號，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束的標志。這樣不符合預期，因此需要修改默認結束命令字符。 DELIMITER //就是將結束命令字符修改為//。調用存儲過程的命令為：call 存儲過程名稱。
#此時的命令的結束符號為// 不是;
mysql> call queryName()//
+--------------+
| name |
+--------------+
| StephenWang7 |
| StephenWang8 |
+--------------+
2 rows in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)
創建帶參數的存儲過程
示例5：根據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
如果想創建存儲過程的內容可以先刪除再重新創建存儲過程。
查看存儲過程
show create procedure <過程名稱>
-> //
+---------------+-------------------------------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+--------------------+
| 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
自定義函數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、調用方式不同
#自定義函數
select <函數名>
#存儲過程
call <存儲過程名>
b、自定義函數不能有輸出參數，而存儲過程可以。
c、自定義函數必須要包含return語句，而存儲過程則不需要。