游标中嵌套有其他查询时要注意的问题

有如下存储过程：

BEGIN
    DECLARE assetId VARCHAR(16);

	DECLARE loadAverage1 FLOAT(10,2) DEFAULT 0;
	DECLARE loadAverage15 FLOAT(10,2) DEFAULT 0;
	DECLARE loadAverageCount INT;
    
    DECLARE loadResult_Tmp VARCHAR(8192) DEFAULT '';

    DECLARE LoadAverageCursorDone INT DEFAULT 0;
    DECLARE LoadAverageCursor CURSOR FOR SELECT Asset_Id, Load_Average_1, Load_Average_15, Load_Average_Count from Load_Average_Info_Tmp;
    DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET LoadAverageCursorDone = 1;

    OPEN LoadAverageCursor;
    LoadAverageCursorLoop:LOOP
        FETCH LoadAverageCursor INTO assetId, loadAverage1, loadAverage15, loadAverageCount;
        IF LoadAverageCursorDone = 1 THEN
            LEAVE LoadAverageCursorLoop;
        END IF;

        SELECT Check_Result INTO loadResult_Tmp FROM Stat_CPU_All_Info_Tmp WHERE Asset_Id = assetId;

        /*
        ...
        */

    END LOOP;
    CLOSE LoadAverageCursor;
END;

 定义了一个游标用来遍历Load_Average_Info_Tmp表，每取得其中的一条数据根据取得的assetId查询Stat_CPU_All_Info_Tmp表。

 

此时遇到一个问题，Load_Average_Info_Tmp表没有遍历完提前退出了循环。

 

问题在游标里面的那条select语句：

SELECT Check_Result INTO loadResult_Tmp FROM Stat_CPU_All_Info_Tmp WHERE Asset_Id = assetId;

当游标中的这条SELECT语句查询结果为空时，会抛出一个'02000'状态而使得LoadAverageCursorDone=1，从而使得循环结束。

 

解决办法：

1.修改引起问题的SELECT语句，使其查询结果永远不为空：

SELECT Check_Result, COUNT(*) INTO loadResult_Tmp, infoCnt FROM Stat_CPU_All_Info_Tmp WHERE Asset_Id = assetId;

 将COUNT(*)查询出来，即使结果集为空，也会输出一条记录。

 修改后的完整语句：

BEGIN
    DECLARE assetId VARCHAR(16);

	DECLARE loadAverage1 FLOAT(10,2) DEFAULT 0;
	DECLARE loadAverage15 FLOAT(10,2) DEFAULT 0;
	DECLARE loadAverageCount INT;
    
    DECLARE loadResult_Tmp VARCHAR(8192) DEFAULT '';
	DECLARE infoCnt INT;

    DECLARE LoadAverageCursorDone INT DEFAULT 0;
    DECLARE LoadAverageCursor CURSOR FOR SELECT Asset_Id, Load_Average_1, Load_Average_15, Load_Average_Count from Load_Average_Info_Tmp;
    DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET LoadAverageCursorDone = 1;

    OPEN LoadAverageCursor;
    LoadAverageCursorLoop:LOOP
        FETCH LoadAverageCursor INTO assetId, loadAverage1, loadAverage15, loadAverageCount;
        IF LoadAverageCursorDone = 1 THEN
            LEAVE LoadAverageCursorLoop;
        END IF;

        SELECT Check_Result, COUNT(*) INTO loadResult_Tmp, infoCnt FROM Stat_CPU_All_Info_Tmp WHERE Asset_Id = assetId;

        /*
        ...
        */

    END LOOP;
    CLOSE LoadAverageCursor;
END;

 

2.第二种办法是不使用游标，改用临时表替代，方法请见Mysql存储过程优化——使用临时表代替游标