MySQL函数和存储过程

函数

数据库中的函数是一种可重复使用的命名代码块，用于在数据库中执行特定的操作或计算。
在MySQL中提供了很多函数，为我们的SQL提供了便利

• 内置函数

mysql> select count(r_id),max(r_id),min(r_id),avg(r_id) from resume_library;
+-------------+-----------+-----------+------------+
| count(r_id) | max(r_id) | min(r_id) | avg(r_id)  |
+-------------+-----------+-----------+------------+
|       26764 |     27195 |         1 | 13491.3612 |
+-------------+-----------+-----------+------------+
1 row in set (0.03 sec)mysql> select r_id,reverse(姓名) from resume_library where 姓名 like '于金_';
+-------+---------------+
| r_id  | reverse(姓名) |
+-------+---------------+
|   285 | 曼金于        |
| 20499 | 淼金于        |
|   286 | 龙金于        |
+-------+---------------+
3 rows in set (0.00 sec)mysql> select r_id,concat('阿龙','真帅'),now(),date_format(now(),'%Y-%m-%d %H:%i:%s') from resume_library where r_id=1;+------+-----------------------+---------------------+----------------------------------------+
| r_id | concat('阿龙','真帅') | now()               | date_format(now(),'%Y-%m-%d %H:%i:%s') |
+------+-----------------------+---------------------+----------------------------------------+
|    1 | 阿龙真帅              | 2024-09-22 17:30:22 | 2024-09-22 17:30:22                    |
+------+-----------------------+---------------------+----------------------------------------+
1 row in set (0.00 sec)-- 字符拼接
mysql> select concat('阿龙','真帅');
+-----------------------+
| concat('阿龙','真帅') |
+-----------------------+
| 阿龙真帅              |
+-----------------------+
1 row in set (0.00 sec)-- 睡眠5秒
mysql> select sleep(5);
+----------+
| sleep(5) |
+----------+
|        0 |
+----------+
1 row in set (5.00 sec)

• 创建函数

-- 更改结束标志符号，方便创建函数
mysql> delimiter $$
mysql> create function f1()->     returns int-> begin->     declare num int;->     declare minid int;->     declare maxid int;->     select max(r_id) from resume.resume_library into maxid;->     select min(r_id) from resume.resume_library into minid;->     set num = maxid + minid;->     return (num);-> end $$
Query OK, 0 rows affected (0.00 sec)
-- 更改结束标志符号
mysql> delimiter ;

• 执行函数

select f1() from resume.resume_library;

• 删除函数

mysql> drop function f1;
Query OK, 0 rows affected (0.00 sec)

存储过程

存储过程，是一个存储MySQL中上sql语句的集合，当主动去调用存储过程时，其中内部的sql语句按照逻辑执行。

• 创建存储过程

mysql> create procedure p1()-> begin-> select * from t3;-> end $$
Query OK, 0 rows affected (0.00 sec)

• 执行存储过程

call p1();

• Python程序执行存储过程

# -*- coding: UTF-8 -*-
"""
@Project ：lufei-learning-city 
@File    ：存储过程.py
@IDE     ：PyCharm 
@Author  ：于金龙@阿龙的代码在报错
@Date    ：2024/9/22 下午6:29 
"""
import pymysqlconn = pymysql.connect(host='localhost',port=3306,user='root',password='20020115',db='resume',charset='utf8'
)
cursor = conn.cursor()cursor.callproc('p1')
result = cursor.fetchall()
cursor.close()
conn.close()
print(result)

• 删除存储过程

mysql> drop procedure p1;
Query OK, 0 rows affected (0.00 sec)

参数类型

存储过程的参数可以分为三种类型：

• in,仅用于传入参数
• out,仅用于返回参数
• inout,既可以传入又可以当做返回值

use user;
-- 更改结束标识符
delimiter $$
create procedure p2(in i1 int,in i2 int,inout i3 int,out r1 int
)
begindeclare temp1 int;declare temp2 int default 0;set temp1 = 1;set r1 = i1 + i2 + temp1 + temp2;set i3 = i3 + 100;
end $$-- 更改结束标识符
delimiter ;

调用存储过程

set @t1=4;
set @t2=0;
call p2(1,2,@t1,@t2)
select @t1,@t2

python进行执行

# -*- coding: UTF-8 -*-
"""
@Project ：lufei-learning-city 
@File    ：存储过程.py
@IDE     ：PyCharm 
@Author  ：于金龙@阿龙的代码在报错
@Date    ：2024/9/22 下午6:29 
"""
import pymysqlconn = pymysql.connect(host='localhost',port=3306,user='root',password='20020115',db='user',charset='utf8'
)
cursor = conn.cursor()# cursor.callproc('p1')
# result = cursor.fetchall()cursor.callproc('p2', args=(1, 22, 3, 4))
table = cursor.fetchall()cursor.execute('select @_p2_0,@_p2_1,@_p2_2,@_p2_3')
result = cursor.fetchall()cursor.close()
conn.close()
print(result)

返回值和返回集

• 创建存储过程

delimiter $$create procedure p3(in n1 int,inout n2 int,out n3 int
)
beginset n2 = n1 + 100;set n3 = n2 + n1 + 100;select * from girl;
end $$
delimiter ;

set @t1 = 4;
set @t2 = 0;
call p3(1, @t1, @t2);
select @t1, @t2;

# -*- coding: UTF-8 -*-
"""
@Project ：lufei-learning-city 
@File    ：存储过程.py
@IDE     ：PyCharm 
@Author  ：于金龙@阿龙的代码在报错
@Date    ：2024/9/22 下午6:29 
"""
import pymysqlconn = pymysql.connect(host='localhost',port=3306,user='root',password='20020115',db='user',charset='utf8'
)cursor = conn.cursor()
cursor.callproc('p3', args=(22, 3, 4))
table = cursor.fetchall()  # 执行过程中的结果集
# 获取执行完存储参数
cursor.execute('select @_p3_0,@_p3_1,@_p3_2')
result = cursor.fetchall()cursor.close()
conn.close()
print(result)
print(table)

• 事务和异常

事务，成功都成功，失败都失败

delimiter $$
create procedure p4(out p_return_code tinyint
)
begindeclare exit handler for sqlexceptionbegin-- errorset p_return_code = 1;rollback;end;declare exit handler for sqlwarningbegin-- waringset p_return_code = 2;rollback;end;start transaction ; -- 开启事务delete from girl;insert into girl(name) values ('1');commit; -- 提交事务set p_return_code = 0;
end $$
delimiter ;

python进行执行

# -*- coding: UTF-8 -*-
"""
@Project ：lufei-learning-city 
@File    ：存储过程.py
@IDE     ：PyCharm 
@Author  ：于金龙@阿龙的代码在报错
@Date    ：2024/9/22 下午6:29 
"""
import pymysqlconn = pymysql.connect(host='localhost',port=3306,user='root',password='20020115',db='user',charset='utf8'
)
cursor = conn.cursor()cursor.callproc('p4', args=(100,))
cursor.execute("select @_p4_0")
result = cursor.fetchall()
cursor.close()
conn.close()
print(result)

油标和存储过程

delimiter $$create procedure p5()
begindeclare sid int;declare sname varchar(50);declare done int default false;-- 声明油标declare my_cursor cursor for select id, namefrom girl;declare continue handler for NOT FOUND set done = TRUE;OPEN my_cursor;xxoo:loopfetch my_cursor into sid,sname;if done thenleave xxoo;end if;insert into t1(name) values (sname);end loop xxoo;close my_cursor;
end $$
delimiter ;call p5();