Question

我有下表Tracking：

+----------+------------+-----------+---------+
| DeviceID | DeviceName | PageCount | JobType |
+----------+------------+-----------+---------+
|        1 | Device1    |        22 | print   |
|        2 | Device2    |        43 | copy    |
|        1 | Device1    |        11 | copy    |
|        2 | Device2    |        15 | print   |
|        3 | Device3    |        65 | copy    |
|        4 | Device4    |         1 | copy    |
|        3 | Device3    |        17 | copy    |
|        2 | Device2    |       100 | copy    |
|        1 | Device1    |       632 | print   |
|        2 | Device2    |         2 | print   |
|        3 | Device3    |        57 | print   |
+----------+------------+-----------+---------+

我正在尝试使用每个设备的总副本和打印创建输出查询，如下例所示：

+------------+------+-------+
| DeviceName | Copy | Print |
+------------+------+-------+
| Device1    |   11 |   654 |
| Device2    |  143 |    17 |
| Device3    |   82 |    57 |
| Device4    |    1 |     0 |
+------------+------+-------+

你能给我一个提示吗？

谢谢。

Answer 1

我能想到的最简单的方法是：

SELECT DeviceName,
       SUM(CASE WHEN JobType = 'copy' THEN PageCount ELSE 0 END) AS Copy,
       SUM(CASE WHEN JobType = 'print' THEN PageCount ELSE 0 END) AS Print
FROM Tracking
GROUP BY DeviceName

Answer 2

您需要做的是： 1.获取pageCount的总和以供复制 2.获取pageCount的总和以进行打印 3.加入两个结果

获得总和很简单，只需要：

1) select DeviceName, sum(pageCount) as copy from Tracking where jobType = 'copy' group by deviceName

2) select DeviceName, sum(pageCount) as print from Tracking where jobType = 'print' group by deviceName

加入他们：

select A.deviceName, copy, print from 
(select DeviceName, sum(pageCount) as copy from Tracking 
where jobType = 'copy' group by deviceName) as A 
inner join
(select DeviceName, sum(pageCount) as print from Tracking 
where jobType = 'print' group by deviceName) as B
ON A.deviceName = B.deviceName

Answer 3

不是三列，而是

select DeviceName, JobType, sum(PageCount) as count 
from table  
group by DeviceName, JobType

SQL - 同一个表上的多个查询

3 个答案: