选择预定义数量的不同值的所有行

Question

我有一个User表，其中包含以下行

id: 1, favorite_id: 1
id: 2, favorite_id: 2
id: 3, favorite_id: 2
id: 4, favorite_id: 3
id: 5, favorite_id: 3
id: 6, favorite_id: 3
id: 7, favorite_id: 4
id: 8, favorite_id: 4
id: 9, favorite_id: 4

并寻找一个查询，该查询返回前3个不同的favorite_id的行=>

id: 1, favorite_id: 1
id: 2, favorite_id: 2
id: 3, favorite_id: 2
id: 4, favorite_id: 3
id: 5, favorite_id: 3
id: 6, favorite_id: 3

Answer 1

• 您可以在Derived Table中获取前3个唯一的favorite_id值
• 将此加入主表以获取所有对应的行。

尝试：

SELECT t.*
FROM `User` t
JOIN (SELECT DISTINCT favorite_id 
      FROM `User`
      ORDER BY favorite_id LIMIT 3) AS dt
    ON dt.favorite_id = t.favorite_id

Answer 2

如果用“前三个”表示按顺序Deferred<T>出现的前三个，则

id

如果仅表示select u.* from (select u.favorite_id, min(id) as min_id from users u group by u.favorite_id order by min_id asc limit 3 ) f3 join users u on f3.favorite_id = u.favorite_id; 的三个最低值，那么Madhur的解决方案就可以了。