MySQL stored procedures and triggers

MySql：

View all stored procedures show procedure status;

View stored procedures in a database: show procedure status where db = ' database name ';

View the creation code of a stored procedure: show create procedure pro_test( stored procedure name );

First, the stored procedure

The basic format of a stored procedure is as follows:

--declaration terminator 
-- create stored procedure 
DELIMITER $   -- declare the terminator of the stored procedure CREATE PROCEDURE pro_test () --stored     procedure name (parameter list) BEGIN --can write multiple sql statements; -- sql statement + process Control SELECT * FROM employee;
 END $   -- end terminator
 

    
      

--Execute stored procedure 
CALL pro_test();    -- CALL stored procedure name (parameters);

--delete the stored procedure 
DROP  PROCEDURE pro_test ;

parameter:
IN : Indicates the input parameter, which can carry data in the stored procedure
OUT: Indicates output parameters, which can return results from stored procedures
INOUT: Indicates input and output parameters, which can either input functions or output functions

1. Stored procedure with input parameters

Requirement: Pass in an employee's id to query employee information

DELIMITER $
CREATE PROCEDURE pro_findById(IN eid INT)  -- IN: 输入参数
BEGIN
    SELECT * FROM employee WHERE id=eid;
END $ 

--call CALL 
pro_findById( 4 );

2. Stored procedure with output parameters

DELIMITER $
CREATE PROCEDURE pro_testOut(OUT str VARCHAR(20))  -- OUT：输出参数
BEGIN
        -- 给参数赋值
    SET str='hellojava';
END $

如何接受返回参数的值呢？这里涉及到MySQL的变量

MySQL变量一共有三种：

全局变量

全局变量又叫内置变量，是mysql数据库内置的变量，对所有连接都起作用。

查看所有全局变量： show variables

查看某个全局变量： select @@变量名

修改全局变量： set 变量名=新值

character_set_client: mysql服务器的接收数据的编码

character_set_results：mysql服务器输出数据的编码

会话变量

只存在于当前客户端与数据库服务器端的一次连接当中。如果连接断开，那么会话变量全部丢失！

定义会话变量: set @变量=值

查看会话变量： select @变量

局部变量

在存储过程中使用的变量就叫局部变量。只要存储过程执行完毕，局部变量就丢失。

回到上面这个存储过程，如何接受返回参数的值呢？

定义一个会话变量name, 使用name会话变量接收存储过程的返回值

CALL pro_testOut(@NAME);

查看变量值

SELECT @NAME;

3. 带有输入输出参数的存储过程

DELIMITER $
CREATE PROCEDURE pro_testInOut(INOUT n INT)  -- INOUT： 输入输出参数
BEGIN
   -- 查看变量
   SELECT n;
   SET n =500;
END $

-- 调用
SET @n=10;

CALL pro_testInOut(@n);

SELECT @n;

4. 带有条件判断的存储过程

需求：输入一个整数，如果1，则返回“星期一”,如果2，返回“星期二”,如果3，返回“星期三”。其他数字，返回“错误输入”;

DELIMITER $
CREATE PROCEDURE pro_testIf(IN num INT,OUT str VARCHAR(20))
BEGIN
    IF num=1 THEN
        SET str='星期一';
    ELSEIF num=2 THEN
        SET str='星期二';
    ELSEIF num=3 THEN
        SET str='星期三';
    ELSE
        SET str='输入错误';
    END IF;
END $

--调用
CALL pro_testIf(4,@str);
 
SELECT @str;

5. 带有循环功能的存储过程

需求：输入一个整数，求和。例如，输入100，统计1-100的和

DELIMITER $
CREATE PROCEDURE pro_testWhile(IN num INT,OUT result INT)
BEGIN
    -- 定义一个局部变量
    DECLARE i INT DEFAULT 1;
    DECLARE vsum INT DEFAULT 0;
    WHILE i<=num DO
          SET vsum = vsum+i;
          SET i=i+1;
    END WHILE;
    SET result=vsum;
END $

--调用
CALL pro_testWhile(100,@result);

SELECT @result;

6. 使用查询的结果赋值给变量（INTO）

DELIMITER $
CREATE PROCEDURE pro_findById2(IN eid INT,OUT vname VARCHAR(20) )
BEGIN
    SELECT empName INTO vname FROM employee WHERE id=eid;
END $

--调用
CALL pro_findById2(1,@NAME);

SELECT @NAME;

7. 带有游标的存储过程

drop procedure if exists pro_test3 ;
DELIMITER $
create procedure pro_test3()
begin 
	declare v_noDataFound int default 0;
	declare v_loginName,v_showName varchar(50);
	declare my_cursor CURSOR for SELECT loginName,showName from users;  -- 定义游标
	declare continue handler for NOT FOUND  set v_noDataFound = 1; -- 游标针对 notfound 的处理
	create temporary table temp_users (  -- 创建临时表
		id int AUTO_INCREMENT,
		temp_loginName varchar(50),
		temp_showName varchar(50),
		primary key (id)
	);
	open my_cursor;
		FETCH my_cursor into v_loginName,v_showName;
		REPEAT
		
			INSERT into temp_users (temp_loginName,temp_showName) VALUES(v_loginName,v_showName);
			FETCH my_cursor into v_loginName,v_showName;
			until v_noDataFound = 1    --  此处结尾没有分号  “;”
		END REPEAT;
	close my_cursor;
	
	-- SELECT temp_loginName,temp_showName from temp_users;
	SELECT * from temp_users;
	drop table temp_users;
end $
DELIMITER ;

二、触发器

触发器作用：当操作了某张表时，希望同时触发一些动作/行为，可以使用触发器完成。

需求：当向员工表插入一条记录时，希望mysql自动同时往日志表插入数据

CREATE TRIGGER tri_empAdd AFTER INSERT ON employee FOR EACH ROW    -- 当往员工表插入一条记录时
     INSERT INTO test_log(content) VALUES('员工表插入了一条记录');

以上触发器是基于insert的，以下两个是基于update和delete的。

-- 创建触发器(修改)
CREATE TRIGGER tri_empUpd AFTER UPDATE ON employee FOR EACH ROW    -- 当往员工表修改一条记录时
     INSERT INTO test_log(content) VALUES('员工表修改了一条记录');
 
-- 创建触发器(删除)
CREATE TRIGGER tri_empDel AFTER DELETE ON employee FOR EACH ROW    -- 当往员工表删除一条记录时
     INSERT INTO test_log(content) VALUES('员工表删除了一条记录');

说明：

1. MySQL uses a semicolon, that is, ";", as a statement separator by default. If this is the case, a stored procedure will be difficult to create properly, because it can be any number of SQL statements between BEGIN and END, and each SQL statement ends with a semicolon. Therefore, when creating a stored procedure, you must redefine the delimiter. In the above use cases, "$" is used as the new delimiter. Note that after the stored procedure is created, the original delimiter ";" must be reset.

The above is based on the MySQL-related content of the Chuanzhi Podcast JAVA employment class video.

Reference: http://www.cnblogs.com/ivictor/p/5045378.html

mysql stored procedure trigger

MySQL stored procedures and triggers

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