游标SQL Server很慢

Question

我不知道为什么这么慢

DECLARE kursor CURSOR FOR
    SELECT mediatime, ShortDate, MediaDateID, TimeID 
    FROM DateTimeMCross

DECLARE @mediatime INT, @ShortDate DATE, @MediaDateID INT, @TimeID INT, @tmpDate DATE

SET @mediatime = 0;

OPEN kursor

FETCH NEXT FROM kursor INTO @mediatime, @ShortDate, @MediaDateID, @TimeID

WHILE @@FETCH_STATUS = 0
BEGIN
    /*SET @tmpDate = (select DATEADD(day,-1,@shortDate))*/
    IF @mediatime >= 2400
    BEGIN
        UPDATE DateTimeMCross
        SET DateTimeMCross.newMediaDateID = 2/*(SELECT     YEAR(@tmpDate) * 10000 + MONTH(@tmpDate) * 100 + DAY(@tmpDate))*/
        WHERE DateTimeMCross.MediaDateID = @MediaDateID 
          AND DateTimeMCross.TimeID = @TimeID
    END
    ELSE IF @mediatime < 2400 AND @mediatime >= 0
    BEGIN
        UPDATE DateTimeMCross
        SET DateTimeMCross.newMediaDateID = @MediaDateID
        WHERE DateTimeMCross.MediaDateID = @MediaDateID 
          AND DateTimeMCross.TimeID = @TimeID
    END

    FETCH NEXT FROM kursor INTO @mediatime, @ShortDate, @MediaDateID, @TimeID
END

CLOSE kursor
DEALLOCATE kursor

我用光标在一个语句之前制作它很快,这真的很慢.

我一开始以为它是由DATEADD()其他功能引起的,但没有.评论之后它和以前一样慢

Answer 1

这实际上根本不需要是光标.好像你想要一个简单的UPDATE:

UPDATE DateTimeMCross
SET newMediaDateID = CASE 
                        WHEN mediatime >= 2400 THEN 2
                        ELSE MediaDateID
                     END
;