本文介绍了SQL 选择连接帮助的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我在找出针对此场景的查询时遇到问题.我想在这个查询中使用两个表，它们是这样的:
I'm having problems figuring out a query for this scenario. I have two tables I want to use in this query, they are like this:
Units
ID
Other Data
People
ID
UnitID <-- fk to Units
Other Data
这就是我想做的:
我想选择在 People 表中没有与它们链接的行的所有单位.我该怎么做?
This is what I want to do:
I want to select all the units that do NOT have a row in the People table linked to them. How can I do this?
推荐答案
SELECT Units.* FROM Units LEFT JOIN People ON People.UnitID = Units.ID WHERE People.ID IS NULL
或者替代
SELECT Units.* FROM Units WHERE NOT EXISTS (SELECT 1 FROM People WHERE People.UnitID = Units.ID)
甚至
SELECT Units.* FROM Units WHERE Units.ID NOT IN (SELECT UnitID FROM People)
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