我想使用类似于以下的查询来检索events
中的所有行,这些行至少有一个对应event_attendances
和'male'
的'female'
行。以下查询不返回任何行(其中肯定有一些events
具有来自两个性别的event_attendances
)。
有没有一种方法可以在没有子查询的情况下执行此操作(由于在我的应用程序中生成SQL的方式,子查询对我来说实现起来要困难得多)?
SELECT * FROM events e
LEFT JOIN event_attendances ea ON (e.id = ea.event_id)
GROUP BY e.id
HAVING ea.gender = 'female' AND ea.gender = 'male'
使用
HAVING sum(ea.gender = 'female') > 0
AND sum(ea.gender = 'male') > 0
要么
HAVING count(distinct ea.gender) = 2
顺便说一句,你应该使用子查询来获取分组时的所有数据。
SELECT *
FROM events
where id in
(
SELECT events.id
FROM events
LEFT JOIN event_attendances ON (events.id = event_attendances.event_id)
GROUP BY events.id
HAVING count(distinct event_attendances.gender) = 2
)
HAVING
通常与聚合函数一起使用。
你应该做self-join
to得到想要的结果,因为ea.gender = 'female' AND ea.gender = 'male'
是矛盾的,它总是返回空集。
你可以试试这个
SELECT T1.*
FROM events T1
INNER JOIN
(SELECT events.id
FROM events
LEFT JOIN event_attendances ON (events.id = event_attendances.event_id)
GROUP BY events.id
HAVING COUNT(DISTINCT event_attendances.gender) = 2) T2 ON T1.events.id=T1.events.id
希望这可以帮助。