mysql - 如何一对多地计算2个表中的 'many-side'实体

Question

我有 2 个与 MySQL 中的“一对多”关系相关的表。如何从表一(“单侧”)中选择 ID，在表二(“多侧”)中具有恰好 N 相关值。我尝试使用:

 SELECT target_id, COUNT(`target_id`) AS counter FROM `many_side_table` WHERE counter = N GROUP BY target_id; 

 SELECT target_id, COUNT(`target_id`) FROM `many_side_table` WHERE COUNT(`target_id`) = N GROUP BY target_id; 

但是这是错误的...

Answer 1

我认为您只需要 having 子句:

SELECT target_id, COUNT(`target_id`)
FROM `many_side_table`
GROUP BY target_id
HAVING COUNT(`target_id`) = N;