Question

我正在尝试将结果分成不同的栏目，我已经搜索了几天，但找不到我想做的正确术语。我可能使用错误的关键词。

我有一张这样的表：

Timestamp    System    Value
1             1          13
1             2          12
1             3          5
2             1          37
2             2          12
2             3          55
3             1          12
3             2          45
3             3          45

我希望得到这样的结果：

Timestamp, System1val, System2val, System3val
1             13            12        5
2             37            12        55
3             12            45        45

我很确定它可以做到。我一直在使用：

SELECT  
    FROM_UNIXTIME(timestamp) as time,  
    CASE System
        WHEN '1' THEN System
        END AS System1val,
    CASE System
        WHEN '2' THEN pyr.measure_conv
        END AS System2val,
    CASE System
        WHEN '3' THEN pyr.measure_conv
        END AS System3val
FROM

这实际上返回不同的字段并填入NULL值。最终目标是按时间戳分组并具有所有三个值

Answer 1

这是一个“交叉表”挑战。你需要以这种方式构建东西......

SELECT
Timestamp,
SUM(CASE WHEN System=X THEN Value ELSE 0 END) AS X,
SUM(CASE WHEN System=Y THEN Value ELSE 0 END) AS Y
FROM System
GROUP BY Timestamp

Answer 2

尝试

SELECT  
    timestamp time,  
    SUM(CASE WHEN system = 1 THEN value ELSE NULL END) System1val,
    SUM(CASE WHEN system = 2 THEN value ELSE NULL END) System2val,
    SUM(CASE WHEN system = 3 THEN value ELSE NULL END) System3val
FROM Table1
 GROUP BY timestamp

输出：

| TIME | SYSTEM1VAL | SYSTEM2VAL | SYSTEM3VAL |
-----------------------------------------------
|    1 |         13 |         12 |          5 |
|    2 |         37 |         12 |         55 |
|    3 |         12 |         45 |         45 |

这是 SQLFiddle 演示

MySQL选择将结果拆分到不同列的位置

2 个答案: