帮助AND&而不是结果 [英] Help with AND & AND NOT results

问题描述

运行时：

WHERE     (VT_TR.QID = 'D')
      AND (VT_TR.AP_DATE < CURRENT_DATE - 1)
      AND (VT_TR.CITY = 'WPG' AND VT_TR.WFR = 'C')

返回两行预计 WFR = C 和 CITY = WPG



但是当我改变时：

It returns two rows as expected where WFR = C and CITY = WPG

But when I change:

AND NOT ( VT_TR.CITY = 'WPG' AND VT_TR.WFR = 'C')

我希望它排除相同的两行，而不是用以下内容排除任何内容：

WFR = C 和 CITY为空

或

WFR = C 和 CITY = WPG



为什么会这样？

I would expect it to exclude the same two rows, instead it seems to be excluding anything with:
WFR = C and CITY is null
or
WFR = C and CITY = WPG

Why would this be?

推荐答案

您应该阅读本文以了解与Null比较的三值逻辑的SQL实现： SQL中的无效 [ ^ ]

You should read this to understand the SQL implementation of three-valued logic in comparisons with Null: Null in SQL[^]

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