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

 

View Code

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  

            LEAVE cursorLoop;  

        END IF;  

    END LOOP;  

    CLOSE cur;  

END

 

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：1.数据量15万，执行成功，耗时8.928s

View Code

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

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。