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好的，这是我现有的查询，可以满足我的需要。

SELECT C1.id AS id, C1.title AS title, C1.instructor_id AS instructor_id, 
  C1.description AS description, C1.date AS date, C1.starttime AS starttime, 
  C1.endtime AS endtime, C1.training_id AS training_id, C2.name AS name, 
  C2.id AS instructors_id 
FROM trainings C1 
LEFT JOIN instructors C2 ON C1.instructor_id = C2.id

但是，我需要添加一些东西。除了我拥有的表之外，我还有两张表需要比较。

表“培训”有一个培训课程列表，由“id”索引。我还有另一个表“registrations”，其中包含有关哪些用户注册了哪些培训课程的信息，包含 3 列：“id”-索引，“user_id”-注册培训的用户的 ID，以及“course_id” - 培训课程的 ID。

除了我现有的查询之外，我还需要做的是仅选择在该用户的“注册”中没有一行的培训课程。

我希望这是有道理的。谢谢谁能帮忙。我已经尝试了几个小时。查询太大了，我无法保持井井有条并正确思考如何去做。

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1 回答 1

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SELECT C1.id AS id, C1.title AS title, C1.instructor_id AS instructor_id, 
  C1.description AS description, C1.date AS date, C1.starttime AS starttime, 
  C1.endtime AS endtime, C1.training_id AS training_id, C2.name AS name, 
  C2.id AS instructors_id 
FROM trainings C1 
LEFT JOIN instructors C2 ON C1.instructor_id = C2.id
LEFT JOIN registrations C3 ON < Whatever they're connected on >
WHERE C3.id IS NULL

基本上也是这样，并通过asJOIN过滤它会将连接表的列返回为.WHERE ... IS NULLLEFT JOINNULL

于 2012-07-23T08:59:15.800 回答