如何計算3個不同表格中兩列的總值？

Question

例如，我有3個表格; 表1：

+-------+ 
| count | 
+-------+ 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
+-------+ 

表2：

+-------+ 
| count | 
+-------+ 
|  3 | 
|  0 | 
|  0 | 
|  0 | 
|  0 | 
+-------+ 

表3：

+-------+ 
| count | 
+-------+ 
|  1 | 
|  1 | 
|  0 | 
|  0 | 
|  1 | 
+-------+ 

我想計算table1.count + table2.count + table3.count，得到的結果，table_right ：

+-------+ 
| count | 
+-------+ 
|  5 | (1+3+1=5) 
|  1 | (0+0+1=1) 
|  0 | (0+0+0=0) 
|  0 | (0+0+0=0) 
|  4 | (3+0+1=4) 
+-------+ 

但是，如果我用命令：

select table1.count+table2.count+table3.count as total 
from table1,table2,table3; 

結果將成爲：

+-------+ 
| total | 
+-------+ 
|  5 | 
|  4 | 
|  4 | 
|  4 | 
|  7 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  5 | 
|  4 | 
|  4 | 
|  4 | 
|  7 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  4 | 
|  3 | 
|  3 | 
|  3 | 
|  6 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  4 | 
|  3 | 
|  3 | 
|  3 | 
|  6 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  1 | 
|  0 | 
|  0 | 
|  0 | 
|  3 | 
|  5 | 
|  4 | 
|  4 | 
|  4 | 
|  7 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
|  2 | 
|  1 | 
|  1 | 
|  1 | 
|  4 | 
+-------+ 

這不是我想要的結果，如果我嘗試

select distinct table1.count+table2.count+table3.count as total 
from table1,table2,table3; 

我會得到：

+-------+ 
| total | 
+-------+ 
|  5 | 
|  4 | 
|  7 | 
|  2 | 
|  1 | 
|  3 | 
|  6 | 
|  0 | 
+-------+ 

還是不是我想要的結果。我怎麼能得到table_right？

Answer 1

如果添加了一個共同的ID（讓呼叫ID ROWID，並讓我們假設它在每個表上同一名稱），

SELECT t1.count + t2.count + t3.count AS total 
FROM table1 AS t1 
LEFT JOIN table2 AS t2 using (rowId) 
LEFT JOIN table3 AS t3 using (rowId) 

如果你沒有這些ID，所有我能想到的它彙總所有t1然後全部t2然後全部t3並最終將結果加在一起。

SELECT t1+t2+t3 as total 
FROM (SELECT (SELECT SUM(count) from table1) as t1, 
     (SELECT SUM(count) from table2) as t2, 
     (SELECT SUM(count) from table3) as t3 
    ) 

看看這個SQLFiddle

EDIT（2）

添加rowId只是改變表：

ALTER TABLE table1 ADD COLUMN rowId int not null auto_increment primary key; 
ALTER TABLE table2 ADD COLUMN rowId int not null auto_increment primary key; 
ALTER TABLE table3 ADD COLUMN rowId int not null auto_increment primary key;