MySQL的选择计算2场基于其他领域

Question

比方说，我有这样的

| user | symbol | status | value | 
---------------------------------- 
| 101 | A  | 1  | 20 | 
| 102 | A  | 1  | 20 | 
| 103 | A  | 1  | 20 | 
| 101 | A  | 0  | 20 | 
| 102 | B  | 1  | 20 | 
| 103 | A  | 1  | 20 | 
| 101 | A  | 0  | 20 | 
| 102 | A  | 1  | 20 | 
| 103 | A  | 0  | 20 | 
| 101 | B  | 1  | 20 | 
| 102 | A  | 0  | 20 | 

一个表，我想这样的结果（所有的值更改为零下具有状态= 0）

| user | symbol | differences | 
---------------------------------- 
| 101 | A  | -20   | 
| 101 | B  | 20   | 
| 102 | A  | 20   | 
| 102 | B  | 20   | 
| 103 | A  | 20   | 

请帮助，任何帮助，将不胜感激！

Answer 1

使用CASE表达式用于改变值减去如果status = 0

查询

select `user`, `symbol`, 
sum(case when `status` = 0 then `value` * -1 else `value` end) as differences 
from `your_table_name` 
group by `user`, `symbol` 
order by `user`, `symbol`; 

SQL Fiddle demo

Answer 2

下面使用CASE..WHEN一个通用的解决方案：在这种特殊情况下

SELECT user, 
     symbol, 
    CASE WHEN status > 0 THEN value 
     ELSE -value END as differences 
FROM yourTable; 

虽然，你也可以使用数学：

SELECT user, 
     symbol, 
     (value * (2*status-1)) as differences 
    FROM yourTable; 

如果你也想聚集的结果，那么你可以改变以上查询使用GROUP BY和SUM作为聚合：

SELECT user, 
     symbol, 
    SUM(CASE WHEN status > 0 THEN value 
     ELSE -value END) as differences 
FROM yourTable 
GROUP BY user, symbol; 

以及等效聚合的查询，使用算术：

SELECT user, 
     symbol, 
     SUM(value * (2*status-1)) as differences 
    FROM yourTable 
GROUP BY user, symbol;