从表A和B中选择，表C和表B中的记录不存在？(Select from table A and B, where records from table A and table B don't exist in table C?)

 我无法查看我想要创建的查询的设置。 
 
 我有表A（用户）和表B（事件）。 对于每一个事件，我想要一个没有参加的用户列表。 
 
 我想第三个表是必要的，将用户与事件关联起来，同时包含用户和事件ID。 如果表中没有用户和事件ID组合，则用户没有参加。 
 
 我的查询如何查看，以便返回每个未参加每个活动的用户列表？ 
 
 或者，我可以查询事件表，循环查看结果，并且对于每个事件，我可以查询第三个表中没有匹配事件ID的记录的用户。 这看起来效率很低，显然是错误的，因为有很多额外的db调用。 
 
foreach ($getEvents as $v) {
    SELECT userID FROM users WHERE userID NOT IN (SELECT userID FROM tableC WHERE eventID = '".$v["eventID"]."');
}
 
 如有需要，欢迎提供更多信息。 

I'm having trouble visualising the setup for a query I'd like to create.
 
I have table A (users) and table B (events). For every event, I would like a list of users who did NOT attend.
 
I imagine a third table is necessary, associating the users with the events, containing both the user and event ID. If a user and event ID combination is absent from the table, the user did not attend.
 
How would my query need to look in order to return a list of every user who did not attend each event?
 
Alternatively I could query the events table, loops through the results, and for each event I could query the users who do not have a record with matching event ID in the third table. This seems inefficient and obviously wrong, as many additional db calls are made.
 
foreach ($getEvents as $v) {
    SELECT userID FROM users WHERE userID NOT IN (SELECT userID FROM tableC WHERE eventID = '".$v["eventID"]."');
}
 
Happy to provide more information if necessary.

原文：https://stackoverflow.com/questions/48179116