【MySQL】Event事件与游标

MySQL的事件就像Linux系统上的定时任务，按照设置的时间或者间隔时间执行设置好的任务。

如果用SQLyog一类的写存储过程、触发器或者事件会省事一些，例如SQLyog就会生成一个大致的模板：

 1 DELIMITER $$

 2 CREATE EVENT `report`.`monitor_user4cx` ON SCHEDULE EVERY 15 MINUTE  DO 

 3 BEGIN

 4 DECLARE cx_id INT(10);

 5 DECLARE t_query VARCHAR(500);

 6 DECLARE done INT DEFAULT FALSE;

 7 DECLARE cur CURSOR FOR SELECT id FROM information_schema.PROCESSLIST WHERE `USER`='cx' AND `TIME` > 600 AND `Command`='Query';

 8 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

 9 OPEN cur;

10 read_loop:LOOP

11 FETCH cur INTO cx_id;

12 IF done THEN

13 LEAVE read_loop;

14 END IF;

15 SELECT t.trx_query,t.trx_started,p.`USER` FROM information_schema.PROCESSLIST p INNER JOIN information_schema.innodb_trx t ON p.id=t.trx_mysql_thread_id WHERE p.id=cx_id INTO @t_query,@t_time,@p_user;

16 INSERT INTO test.monitor_user4cx(`p_id`,`start_time`,`user`,`time`,`query`) VALUES (cx_id,@t_time,@p_user,NOW(),@t_query);

17 KILL cx_id;

18 END LOOP;

19 CLOSE cur;

20 END$$

21 DELIMITER ;

View Code

游标的写法：

CREATE PROCEDURE `test`.`new_procedure` ()

BEGIN

  -- 需要定义接收游标数据的变量 

  DECLARE a CHAR(16);

  -- 声明游标的结束标志

  DECLARE done INT DEFAULT FALSE;

  -- 将所需数据赋予游标，游标必须定义在变量/条件后，handler前；否则会报错。
　-- ERROR 1337 (42000): Variable or condition declaration after cursor or handler declaration
  DECLARE cur CURSOR FOR SELECT i FROM test.t;

  -- 将结束标志绑定到游标，如果捕获到not found异常时就会将变量done设置为TRUE，done=TRUE可以当作循环跳出条件

  DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

  -- 打开游标

  OPEN cur;

  

  -- 开始循环

  read_loop: LOOP

    -- 提取游标里的数据，这里只有一个，也可以有多个，例如fetch <游标名> into <变量1>,<变量2>

    FETCH cur INTO a;

    -- 声明结束的时候

    IF done THEN

      LEAVE read_loop;

    END IF;

 

   -- 这里做你想做的循环的事件

    sql;



  END LOOP;

  -- 关闭游标

  CLOSE cur;



END

游标示例：

1、repeat循环（该循环用do while，先执行后判断）

drop procedure if exists test_proce2;  

create procedure test_proce2()  

begin  

    declare temp_id int(11);  

    declare temp_time datetime;  

    declare isFinished boolean default false;  

    declare test_cursor cursor for select id,time from test;  

    declare continue handler for not found set isFinished=true;  

    open test_cursor;  

    repeat  

        fetch test_cursor into temp_id,temp_time;  

        if not isFinished then  

            select concat(concat(temp_id,":"),temp_time);  

        end if;  

    until isFinished end repeat;  

   close test_cursor;  

  end  

2、loop循环

 drop procedure if exists test_proce3;  

create procedure test_proce3()  

begin  

    declare temp_id int(11);  

    declare temp_time datetime;  

    declare isFinished boolean default false;  

    declare test_cursor cursor for select id,time from test;  

    declare continue handler for not found set isFinished=true;  

    open test_cursor;  

    test_loop:loop  

        fetch test_cursor into temp_id,temp_time;  

        if isFinished then  

            leave test_loop;  

        end if;  

        //若该if语句放在fetch后面，该循环为while型；若该if语句紧接在end loop前该循环为do while型。  

        select concat(concat(temp_id,":"),temp_time);  

    end loop test_loop;  

  close test_cursor;  

 end  

 

示例：

定期检查长时间执行的查询，记录并杀掉

DELIMITER $$

CREATE EVENT `report`.`monitor_user4cx` ON SCHEDULE EVERY 15 MINUTE  DO 

BEGIN

DECLARE cx_id INT(10);

DECLARE t_query VARCHAR(500);

DECLARE done INT DEFAULT FALSE;

DECLARE cur CURSOR FOR SELECT id FROM information_schema.PROCESSLIST WHERE `USER`='cx' AND `TIME` > 600 AND `Command`='Query';

DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

OPEN cur;

read_loop:LOOP

FETCH cur INTO cx_id;

IF done THEN

LEAVE read_loop;

END IF;

SELECT t.trx_query,t.trx_started,p.`USER` FROM information_schema.PROCESSLIST p INNER JOIN information_schema.innodb_trx t ON p.id=t.trx_mysql_thread_id WHERE p.id=cx_id INTO @t_query,@t_time,@p_user;

INSERT INTO test.monitor_user4cx(`p_id`,`start_time`,`user`,`time`,`query`) VALUES (cx_id,@t_time,@p_user,NOW(),@t_query);

KILL cx_id;

END LOOP;

CLOSE cur;

END$$

DELIMITER ;

 

语法中变量的使用方法：

### 可以直接用set赋值

set @a=1;

set @b=(select count(*) from information_schema.processlist);

insert into test_db.table1 select @a,@b,now();



### 可以用into将结果集赋值给变量

select id,name,create_time from test_db.table2 into @u_id,@u_name,@u_addtime;

同

select id,name,create_time into @u_id,@u_name,@u_addtime from test_db.table2；

select @u_id,@u_name,@u_addtime;

 

删除事件：

drop event event_name;

 

部分内容转自：

http://www.cnblogs.com/trying/p/3296793.html

http://blog.csdn.net/willchyis/article/details/7943467