DECLARE @tempId NVARCHAR(Max),        @tempIDD uniqueidentifier         WHILE EXISTS ( SELECT UserId               FROM  Users Group By UserId having (count(*))>1 )    BEGIN          SELECT TOP 1 @tempId = UserId                       FROM   (SELECT UserId               FROM  Users Group By UserId having (count(*))>1 ) #cc        Select Top 1 @tempIDD=Id FROM Users where UserId=@tempId        DELETE  FROM Users  WHERE   [id] = @tempIDD             END

 上面这种方式，效率比较低。改进后的方式如下：

Delete From Users WHERE ID in (SELECT min（ID） FROM Users Group By UserId having (count（*))>1 )