如何从2个表中计算“多边”实体一到多个(How to count 'many

如何从2个表中计算“多边”实体一到多个(How to count 'many-side' entities from 2 tables one to many) mysql

我有两个与MySQL中“一对多”关系相关的表。 如何从表一（'单侧'）中选择ID，在表2（'多面'）中具有N个相关值。 我试过用：

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;

但这是错的......

I have 2 tables related with 'one to many' relation in MySQL. How can I select IDs from table one ('one-side') witch has exactly N related values in table two ('many-side'). I tried to use:

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;

But it is wrong...

最满意答案

我想你只想要有条款：

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

I think you just want the having clause:

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