SQLite的 - 由多個列組，計算不同的一個

Question

說我有如下表：

Commit File Past_Author 
1  a  Alice 
1  a  Bob 
1  a  Bob 
1  b  Alice 

我期待數不同的作者對每一個文件，以提交總結的數量。在這種情況下，我希望3個作者提交1（文件a爲2，文件b爲1）。

我想是這樣的：SELECT Commit, SUM(NUM_AUTHORS) FROM (SELECT Commit, File, COUNT(DISTINT Past_Author) as NA FROM COMMITS GROUP BY File) GROUP BY Commit

Answer 1

這應該做的伎倆。

SELECT Commit, SUM(NUM_AUTHORS) FROM 
(
    SELECT 
     Commit, 
     File, 
     COUNT(DISTINCT Past_Author) AS NUM_AUTHORS 
    FROM COMMITS 
    GROUP BY Commit, File 
) AS AUTHOR_COUNT 
GROUP BY Commit;