Mysql存储过程优化——使用临时表代替游标

Mysql游标在操作小数据量时比较方便，效率可观，但操作大数据量，速度比较慢，甚至直接产生系统错误。



一般说来，当操作的数据超过1万条时，就避免用游标吧。



为了测试游标性能，写了下面一个游标对IDC_Gather_Info表中数据进行遍历

Sql代码


CREATE DEFINER=`root`@`%` PROCEDURE `debug`(IN `beginTime` int, IN `checkTime` int)

BEGIN

DECLARE t_id VARCHAR(64) DEFAULT '';

DECLARE t_item TINYINT DEFAULT 0;

DECLARE t_result VARCHAR(8192) DEFAULT '';



DECLARE cursorDone INT DEFAULT 0;

DECLARE cur CURSOR FOR SELECT Asset_Id, Check_Item, Check_Result from IDC_Gather_Info WHERE Check_Time > beginTime AND Check_Time <= checkTime;

DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET cursorDone = 1;



OPEN cur;

cursorLoop:LOOP

FETCH cur INTO t_id, t_item, t_result;

IF cursorDone = 1 THEN

LE***E cursorLoop;

END IF;

END LOOP;

CLOSE cur;

END

下面是当表中数据分别为15万、5万、1万时游标的表现：



1.数据量15万，存储过程执行失败，提示错误：Incorrect key file for table '/tmp/#sql_3044_0.MYI';try to repair it

2.数据量5万，执行成功，耗时31.051s

3.数据量1万，执行成功，耗时1.371s



下面使用临时表替换游标：

Sql代码


CREATE DEFINER=`root`@`%` PROCEDURE `debug`(IN `beginTime` int, IN `checkTime` int)

BEGIN

DECLARE t_id VARCHAR(64) DEFAULT '';

DECLARE t_item TINYINT DEFAULT 0;

DECLARE t_result VARCHAR(8192) DEFAULT '';



DECLARE maxCnt INT DEFAULT 0;

DECLARE i INT DEFAULT 0;



DROP TABLE IF EXISTS Gather_Data_Tmp;

CREATE TEMPORARY TABLE Gather_Data_Tmp(

`Tmp_Id` INT UNSIGNED NOT NULL AUTO_INCREMENT,

`Asset_Id` VARCHAR(16) NOT NULL,

`Check_Item` TINYINT(1) NOT NULL,

`Check_Result` VARCHAR(8192) NOT NULL,

PRIMARY KEY (`Tmp_Id`)

)ENGINE=MyISAM DEFAULT CHARSET=utf8;



SET @tSql = CONCAT('INSERT INTO Gather_Data_Tmp (`Asset_Id`, `Check_Item`, `Check_Result`)

SELECT Asset_Id, Check_Item, Check_Result

FROM IDC_Gather_Info

WHERE Check_Time > ',beginTime,' AND Check_Time <= ',checkTime);

PREPARE gatherData FROM @tSql;

EXECUTE gatherData;



SELECT MIN(`Tmp_Id`) INTO i FROM Gather_Data_Tmp;

SELECT MAX(`Tmp_Id`) INTO maxCnt FROM Gather_Data_Tmp;



WHILE i <= maxCnt DO

SELECT Asset_Id, Check_Item, Check_Result INTO t_id, t_item, t_result FROM Gather_Data_Tmp WHERE Tmp_Id = i;

SET i = i + 1;

END WHILE;

END



1.数据量15万，执行成功，耗时8.928s

2.数据量5万，执行成功，耗时2.994s

3.数据量1万，执行成功，耗时0.634s



可以看到Mysql的游标在处理大一点的数据量时还是比较乏力的，仅适合用于操作几百上千的小数据量。