SQL只顯示前2條評論每個actionid

Question

可能重複：
Selecting the top n rows within a group by clause

，我有以下數據：

id actionid commentid 
1 1  1 
2 1  2 
3 1  3 
4 2  1 

我想創建一個SQL僅顯示每個actionid的前2條評論。在這種情況下，我的SQL應僅返回ID（1,2,4）

感謝

Answer 1

SELECT id, 
     actionid, 
     commentid 
FROM (
    SELECT id, 
      actionid, 
      commentid, 
      row_number() over (partition by actionid order by id) rn 
    FROM your_table 
) t 
WHERE rn <= 2