增加了兩個獨立的表

Question

總和我有兩個表

td_sell

|----------|----------------|------------------| 
| id  | user_id  | price   | 
|----------------------------------------------| 
| 1  |  2   |  10   | 
|----------------------------------------------| 
| 2  |  1   |  5   | 
|----------------------------------------------| 
| 3  |  2   |  3   | 
|----------------------------------------------| 

和td_commsion

|----------|----------------|------------------| 
| id  | user_id  | price   | 
|----------------------------------------------| 
| 1  |  1   |  3   | 
|----------------------------------------------| 
| 2  |  1   |  5   | 
|----------------------------------------------| 
| 3  |  2   |  3   | 
|----------------------------------------------| 

現在

我想要一個SQL查詢這樣

SELECT (SUM(td_sell.price) + SUM(td_comission.price)) AS his_earning 
FROM td_sell, td_comission 
WHERE td_sell.user_id='1' 
AND td_comission.user_id='1' 

但它顯示異常結果

結果應該是13，但其顯示29

Answer 1

你得到笛卡爾的總和加入兩個表。

http://en.wikipedia.org/wiki/Cartesian_product

Answer 2

SELECT sum(price) 
FROM (
    SELECT * FROM td_sell 
    UNION ALL 
    SELECT * FROM td_commission 
) a 
where a.user_id=1 

這裏有一個SQL小提琴： Fiddle

Answer 3

這將工作：

SELECT (SELECT SUM(s.price) FROM td_sell s WHERE s.user_id = 1) 
+ 
(SELECT SUM(c.price) FROM td_comission c WHERE c.user_id = 1) 

DEMO：SqlFiddle

Answer 4

在合併結果之前，您需要分別在每張桌子上完成總和。以下是一種方法：

select (sell + commission) as his_earning 
from (select SUM(td_sell.price) as sell 
     from td_sell 
     where td_sell.user_id='1' 
    ) s cross join 
    (select SUM(td_comission.price) as commission 
     from td_comission 
     where td_comission.user_id='1' 
    ) c