的MySql得到每父ID

Question

ID item_ID parent_ID count 
================================ 
1  11   2   5 
2  12   2   6 
3  13   3   2 
4  14   3   3 
5  15   2   7 
6  16   1   3 

SELECT * FROM relations ORDER BY count DESC

，應該是回報是2,4和6，因爲他們有他們的parent_ID

最高計數行最高計數如何更改查詢到完成這個？

Answer 1

內部選擇得到每個parent_ID的最高計數。如果你加入，它會過濾出相關記錄

select t1.* 
from your_table t1 
join 
(
    select parent_ID, max(count) as mcount 
    from your_table 
    group by parent_ID 
) t2 on t1.parent_ID = t2.parent_ID 
    and t1.count = t2.mcount