mysql获取id数组

Question

所以我有一个包含几张表的数据库。主要是Plant。我还有一个包含 plant_id、effect_id 的 PlantEffects 表。我需要做的是选择 Plants，但根据 PlantEffects.effect_id 选择排名前 5 的 PlantEffects。所以它会出来

|ID|NAME|top_effect_ids|
|1 |abc |1,4,5,6,7     |
|2 |def |3,2,9,7,5     |

Answer 1

如果我对您的问题的理解正确，您希望将前五个 effect_id(按计数)放入 CSV 列表中。

你可以这样做:

SELECT 
    a.id, 
    a.name, 
    SUBSTRING_INDEX(GROUP_CONCAT(b.effect_id ORDER BY b.effectcnt DESC), ',', 5) AS top_effect_ids
FROM 
    plants a
INNER JOIN
(
    SELECT plant_id, effect_id, COUNT(1) AS effectcnt
    FROM planteffects
    GROUP BY plant_id, effect_id
) b ON a.id = b.plant_id
GROUP BY 
    a.id, a.name