Select Distinct Not In Select Distinct 返回 0 行，应该接近 1000

Question

Select Distinct FileId From dbo.Files

returns 3415 行

Select Distinct FileId From dbo.SyncHistory Where Date > '2015/7/1'

returns 2483 行。

Select Distinct FileId From dbo.Files 
Where FileId In (Select Distinct FileId From dbo.SyncHistory Where Date > '2015/7/1')

returns 2482 行。好吧，有人在这个月进行了同步，但我猜后来删除了他们的文件。

但是：

Select Distinct FileId From dbo.Files 
Where FileId NOT In (Select Distinct FileId From dbo.SyncHistory Where Date > '2015/7/1')

Returns 0 行.

我以为我的连接断开了，但我已经运行并重新运行它并且结果是一致的，即使也一直是错误的。这是 sql 错误吗？我在这里错过了什么？

Answer 1

可能与FileId 列中的空值有关。请检查分别执行的内部和外部查询中的空值。如果您发现空值，那么以下应该有效：

Select Distinct FileId From dbo.Files 
Where FileId In (Select Distinct FileId From dbo.SyncHistory Where Date > '2015/7/1' 
AND FileId IS NOT NULL)

Select Distinct FileId From dbo.Files 
Where FileId NOT In (Select Distinct FileId From dbo.SyncHistory Where Date > '2015/7/1' 
AND FileId IS NOT NULL)

Answer 2

尝试

SELECT DISTINCT
a.FileID
FROM dbo.Files a
LEFT JOIN
(Select Distinct FileId From dbo.SyncHistory Where Date > '2015/7/1') b
ON a.FileID = b.FileID
WHERE b.FileID IS NULL

Select Distinct Not In Select Distinct 返回 0 行，应该接近 1000

Select Distinct Not In Select Distinct Returning 0 Rows, Should be almost 1000

tsql

distinct