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问题描述
如果我有两个表：用户和约会。我如何查询数据库以找到如下所示的内容：
If I have two tables: Users and Appointments. How would I query the db to find something like the following:
SELECT * FROM users WHERE (none of: appointments.user = user.id)
我假设我需要一些类型的约会表，确定从哪里开始。
I am assuming I would need some type of join with the appointments table, just not sure where to start.
推荐答案
SELECT * FROM users
LEFT JOIN Appointments ON Users.UserID=Appointments.UserID
WHERE Appointments.UserID is null
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