Mysql存储过程优化——使用临时表代替游标(转)

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

 

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

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。