如何總結列弗朗3個不同的表

Question

我有這樣

select * from t1; 

    ID  SAL 
----- ---------- 
    1  100 
    2  200 
    3  300 

select * from t2; 

    ID  SAL 
------ ---------- 
    1  100 
    2  200 
    3  300 
    4  100 

select * from t3; 

    ID  SAL 
------ ---------- 
    1  100 
    2  200 
    3  300 
    4  100 

一個表，但輸出應該是這樣的：

id   sal 
------------------- 
1   300 
2   600 
3   900 
4   200 

Answer 1

使用UNION ALL與GROUP：

SELECT ID, SUM(SAL) FROM 
(
    SELECT ID, SAL FROM t1 
    UNION ALL 
    SELECT ID, SAL FROM t2 
    UNION ALL 
    SELECT ID, SAL FROM t3 
) AS T 
GROUP BY ID