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【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 $$ 2 CREATE EVENT `report`.`monitor_user4cx` ON SCHEDULE EVERY 15 MINUTE  DO  3 BEGIN 4 DECLARE cx_id INT(10); 5 DECLARE t_query VARCHAR(500); 6 DECLARE done INT DEFAULT FALSE; 7 DECLARE cur CURSOR FOR SELECT id FROM information_schema.PROCESSLIST WHERE `USER`=cx AND `TIME` > 600 AND `Command`=Query; 8 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; 9 OPEN cur;10 read_loop:LOOP11 FETCH cur INTO cx_id;12 IF done THEN13 LEAVE read_loop;14 END IF;15 SELECT t.trx_query,t.trx_started,p.`USER` FROM information_schema.PROCESSLIST p INNER JOIN information_schema.innodb_trx t ON p.id=t.trx_mysql_thread_id WHERE p.id=cx_id INTO @t_query,@t_time,@p_user;16 INSERT INTO test.monitor_user4cx(`p_id`,`start_time`,`user`,`time`,`query`) VALUES (cx_id,@t_time,@p_user,NOW(),@t_query);17 KILL cx_id;18 END LOOP;19 CLOSE cur;20 END$$21 DELIMITER ;
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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 $$CREATE EVENT `report`.`monitor_user4cx` ON SCHEDULE EVERY 15 MINUTE  DO BEGINDECLARE cx_id INT(10);DECLARE t_query VARCHAR(500);DECLARE done INT DEFAULT FALSE;DECLARE cur CURSOR FOR SELECT id FROM information_schema.PROCESSLIST WHERE `USER`=cx AND `TIME` > 600 AND `Command`=Query;DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;OPEN cur;read_loop:LOOPFETCH cur INTO cx_id;IF done THENLEAVE read_loop;END IF;SELECT t.trx_query,t.trx_started,p.`USER` FROM information_schema.PROCESSLIST p INNER JOIN information_schema.innodb_trx t ON p.id=t.trx_mysql_thread_id WHERE p.id=cx_id INTO @t_query,@t_time,@p_user;INSERT INTO test.monitor_user4cx(`p_id`,`start_time`,`user`,`time`,`query`) VALUES (cx_id,@t_time,@p_user,NOW(),@t_query);KILL cx_id;END LOOP;CLOSE cur;END$$DELIMITER ;

 

 

部分内容转自:

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

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

 

【MySQL】Event事件与游标