MySQL---存储过程 及 条件语句循环语句

Posted 2020-12-31 Horror

存储过程

存储过程是一个SQL语句集合，当主动去调用存储过程时，其中内部的SQL语句会按照逻辑执行。

1、创建存储过程

 1 -- 创建存储过程
 2 
 3 delimiter //
 4 create procedure p1()
 5 BEGIN
 6     select * from t1;
 7 END//
 8 delimiter ;
 9 
10 
11 
12 -- 执行存储过程
13 
14 call p1()

无参数存储过程

1 注：
2     delimiter //     设置mysql的截止符为“//”
3 
4     delimiter ;

对于存储过程，可以接收参数，其参数有三类：

• in          仅用于传入参数用
• out        仅用于返回值用
• inout     既可以传入又可以当作返回值

 1 -- 创建存储过程
 2 delimiter  3 create procedure p1(
 4     in i1 int,
 5     in i2 int,
 6     inout i3 int,
 7     out r1 int
 8 )
 9 BEGIN
10     DECLARE temp1 int;
11     DECLARE temp2 int default 0;
12     
13     set temp1 = 1;
14 
15     set r1 = i1 + i2 + temp1 + temp2;
16     
17     set i3 = i3 + 100;
18 
19 end20 delimiter ;
21 
22 -- 执行存储过程
23 set @t1 =4;
24 set @t2 = 0;
25 CALL p1 (1, 2 ,@t1, @t2);
26 SELECT @t1,@t2;

有参数的存储过程

1 delimiter //
2                     create procedure p1()
3                     begin
4                         select * from v1;
5                     end //
6                     delimiter ;

1. 结果集

 1 delimiter //
 2                     create procedure p2(
 3                         in n1 int,
 4                         inout n3 int,
 5                         out n2 int,
 6                     )
 7                     begin
 8                         declare temp1 int ;
 9                         declare temp2 int default 0;
10 
11                         select * from v1;
12                         set n2 = n1 + 100;
13                         set n3 = n3 + n1 + 100;
14                     end //
15                     delimiter ;

2. 结果集+out值

 1 delimiter  2                         create PROCEDURE p1(
 3                             OUT p_return_code tinyint
 4                         )
 5                         BEGIN 
 6                           DECLARE exit handler for sqlexception 
 7                           BEGIN 
 8                             -- ERROR 
 9                             set p_return_code = 1; 
10                             rollback; 
11                           END; 
12                          
13                           DECLARE exit handler for sqlwarning 
14                           BEGIN 
15                             -- WARNING 
16                             set p_return_code = 2; 
17                             rollback; 
18                           END; 
19                          
20                           START TRANSACTION; 
21                             DELETE from tb1;
22                             insert into tb2(name)values(‘seven‘);
23                           COMMIT; 
24                          
25                           -- SUCCESS 
26                           set p_return_code = 0; 
27                          
28                           END29                     delimiter ;

3. 事务

 1 delimiter //
 2                     create procedure p3()
 3                     begin 
 4                         declare ssid int; -- 自定义变量1  
 5                         declare ssname varchar(50); -- 自定义变量2  
 6                         DECLARE done INT DEFAULT FALSE;
 7 
 8 
 9                         DECLARE my_cursor CURSOR FOR select sid,sname from student;
10                         DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
11                         
12                         open my_cursor;
13                             xxoo: LOOP
14                                 fetch my_cursor into ssid,ssname;
15                                 if done then 
16                                     leave xxoo;
17                                 END IF;
18                                 insert into teacher(tname) values(ssname);
19                             end loop xxoo;
20                         close my_cursor;
21                     end  //
22                     delimter ;

4. 游标

 1 delimiter  2 DROP PROCEDURE IF EXISTS proc_sql  3 CREATE PROCEDURE proc_sql ()
 4 BEGIN
 5     declare p1 int;
 6     set p1 = 11;
 7     set @p1 = p1;
 8 
 9     PREPARE prod FROM ‘select * from tb2 where nid > ?‘;
10     EXECUTE prod USING @p1;
11     DEALLOCATE prepare prod; 
12 
13 END14 delimiter ;

5. 动态执行SQL

2、删除存储过程

1 drop procedure proc_name;

3、执行存储过程

 1 -- 无参数
 2 call proc_name()
 3 
 4 -- 有参数，全in
 5 call proc_name(1,2)
 6 
 7 -- 有参数，有in，out，inout
 8 set @t1=0;
 9 set @t2=3;
10 call proc_name(1,2,@t1,@t2)

执行存储过程

 1 #!/usr/bin/env python
 2 # -*- coding:utf-8 -*-
 3 import pymysql
 4 
 5 conn = pymysql.connect(host=‘127.0.0.1‘, port=3306, user=‘root‘, passwd=‘123‘, db=‘t1‘)
 6 cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)
 7 # 执行存储过程
 8 cursor.callproc(‘p1‘, args=(1, 22, 3, 4))
 9 # 获取执行完存储的参数
10 cursor.execute("select @_p1_0,@_p1_1,@_p1_2,@_p1_3")
11 result = cursor.fetchall()
12 
13 conn.commit()
14 cursor.close()
15 conn.close()
16 
17 
18 print(result)

pymysql执行存储过程

条件语句

 1 delimiter  2 CREATE PROCEDURE proc_if ()
 3 BEGIN
 4     
 5     declare i int default 0;
 6     if i = 1 THEN
 7         SELECT 1;
 8     ELSEIF i = 2 THEN
 9         SELECT 2;
10     ELSE
11         SELECT 7;
12     END IF;
13 
14 END15 delimiter ;

if条件语句

循环语句

 1 delimiter  2 CREATE PROCEDURE proc_while ()
 3 BEGIN
 4 
 5     DECLARE num INT ;
 6     SET num = 0 ;
 7     WHILE num < 10 DO
 8         SELECT
 9             num ;
10         SET num = num + 1 ;
11     END WHILE ;
12 
13 END14 delimiter ;

while循环

 1 delimiter  2 CREATE PROCEDURE proc_repeat ()
 3 BEGIN
 4 
 5     DECLARE i INT ;
 6     SET i = 0 ;
 7     repeat
 8         select i;
 9         set i = i + 1;
10         until i >= 5
11     end repeat;
12 
13 END14 delimiter ;

repeat循环

 1 BEGIN
 2     
 3     declare i int default 0;
 4     loop_label: loop
 5         
 6         set i=i+1;
 7         if i<8 then
 8             iterate loop_label;
 9         end if;
10         if i>=10 then
11             leave loop_label;
12         end if;
13         select i;
14     end loop loop_label;
15 
16 END

loop