sql - 表 'dbo.UserProperties' 不明确。为什么会出现这个错误？

Question

为什么这个更新语句没有被编译？根据msdn，这是完全正确的。

UPDATE  dbo.UserProperties
  SET     Value = MergeFrom.Value
FROM    dbo.UserProperties MergeFrom ,
        dbo.UserProperties MergeTo
WHERE   MergeFrom.Field = MergeTo.Field
        AND MergeTo.[Key] = CAST(@MergeToUserID AS NVARCHAR(50))
        AND MergeFrom.[Key] = CAST(@MergeFromUserID AS NVARCHAR(50))

Answer 1

我认为您需要在更新中引用别名以进行自连接。至少我刚刚尝试使用 self JOIN 进行更新，并且以下类型的语法对我有用。

UPDATE  MergeTo
    SET MergeTo.Value = MergeFrom.Value
FROM dbo.UserProperties AS MergeFrom INNER JOIN
          dbo.UserProperties AS MergeTo ON MergeFrom.Field = MergeTo.Field
WHERE   MergeTo.[Key] = CAST(@MergeToUserID AS NVARCHAR(50))
                        AND MergeFrom.[Key] = CAST(@MergeFromUserID AS NVARCHAR(50))