MySQL---存储过程 及 条件语句、循环语句

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

 -- 创建存储过程

 delimiter //
 create procedure p1()
 BEGIN
     select * from t1;
 END//
 delimiter ;

 -- 执行存储过程

 call p1()

无参数存储过程

 注：
     delimiter //     设置mysql的截止符为“//”

     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

 -- 创建存储过程
 delimiter \\
 create procedure p1(
     in i1 int,
     in i2 int,
     inout i3 int,
     out r1 int
 )
 BEGIN
     DECLARE temp1 int;
     DECLARE temp2 int default 0;

     set temp1 = 1;

     set r1 = i1 + i2 + temp1 + temp2;

     set i3 = i3 + 100;

 end\\
 delimiter ;

 -- 执行存储过程
 set @t1 =4;
 set @t2 = 0;
 CALL p1 (1, 2 ,@t1, @t2);
 SELECT @t1,@t2;

有参数的存储过程

 delimiter //
                     create procedure p1()
                     begin
                         select * from v1;
                     end //
                     delimiter ;

1. 结果集

 delimiter //
                     create procedure p2(
                         in n1 int,
                         inout n3 int,
                         out n2 int,
                     )
                     begin
                         declare temp1 int ;
                         declare temp2 int default 0;

                         select * from v1;
                         set n2 = n1 + 100;
                         set n3 = n3 + n1 + 100;
                     end //
                     delimiter ;

2. 结果集+out值

 delimiter \\
                         create PROCEDURE p1(
                             OUT p_return_code tinyint
                         )
                         BEGIN
                           DECLARE exit handler for sqlexception
                           BEGIN
                             -- ERROR
                             set p_return_code = 1;
                             rollback;
                           END; 

                           DECLARE exit handler for sqlwarning
                           BEGIN
                             -- WARNING
                             set p_return_code = 2;
                             rollback;
                           END; 

                           START TRANSACTION;
                             DELETE from tb1;
                             insert into tb2(name)values('seven');
                           COMMIT; 

                           -- SUCCESS
                           set p_return_code = 0; 

                           END\\
                     delimiter ;

3. 事务

 delimiter //
                     create procedure p3()
                     begin
                         declare ssid int; -- 自定义变量1
                         declare ssname varchar(50); -- 自定义变量2
                         DECLARE done INT DEFAULT FALSE;

                         DECLARE my_cursor CURSOR FOR select sid,sname from student;
                         DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

                         open my_cursor;
                             xxoo: LOOP
                                 fetch my_cursor into ssid,ssname;
                                 if done then
                                     leave xxoo;
                                 END IF;
                                 insert into teacher(tname) values(ssname);
                             end loop xxoo;
                         close my_cursor;
                     end  //
                     delimter ;

4. 游标

 delimiter \\
 DROP PROCEDURE IF EXISTS proc_sql \\
 CREATE PROCEDURE proc_sql ()
 BEGIN
     declare p1 int;
     set p1 = 11;
     set @p1 = p1;

     PREPARE prod FROM 'select * from tb2 where nid > ?';
     EXECUTE prod USING @p1;
     DEALLOCATE prepare prod; 

 END\\
 delimiter ;

5. 动态执行SQL

2、删除存储过程

 drop procedure proc_name;

3、执行存储过程

 -- 无参数
 call proc_name()

 -- 有参数，全in
 call proc_name(1,2)

 -- 有参数，有in，out，inout
 set @t1=0;
 set @t2=3;
 call proc_name(1,2,@t1,@t2)

执行存储过程

 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
 import pymysql

 conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', passwd='', db='t1')
 cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)
 # 执行存储过程
 cursor.callproc('p1', args=(1, 22, 3, 4))
 # 获取执行完存储的参数
 cursor.execute("select @_p1_0,@_p1_1,@_p1_2,@_p1_3")
 result = cursor.fetchall()

 conn.commit()
 cursor.close()
 conn.close()

 print(result)

pymysql执行存储过程

条件语句

 delimiter \\
 CREATE PROCEDURE proc_if ()
 BEGIN

     declare i int default 0;
     if i = 1 THEN
         SELECT 1;
     ELSEIF i = 2 THEN
         SELECT 2;
     ELSE
         SELECT 7;
     END IF;

 END\\
 delimiter ;

if条件语句

循环语句

 delimiter \\
 CREATE PROCEDURE proc_while ()
 BEGIN

     DECLARE num INT ;
     SET num = 0 ;
     WHILE num < 10 DO
         SELECT
             num ;
         SET num = num + 1 ;
     END WHILE ;

 END\\
 delimiter ;

while循环

 delimiter \\
 CREATE PROCEDURE proc_repeat ()
 BEGIN

     DECLARE i INT ;
     SET i = 0 ;
     repeat
         select i;
         set i = i + 1;
         until i >= 5
     end repeat;

 END\\
 delimiter ;

repeat循环

 BEGIN

     declare i int default 0;
     loop_label: loop

         set i=i+1;
         if i<8 then
             iterate loop_label;
         end if;
         if i>=10 then
             leave loop_label;
         end if;
         select i;
     end loop loop_label;

 END

loop