将 CASE 与 GROUP BY 一起使用

Question

我在 T-SQL 中有以下查询：

SELECT dbo.table2.device, 
    dbo.table2.CREATETIME AS create_time,
    CASE WHEN dbo.table1.ACTIONID = 1 
        THEN dbo.table1.startstop 
    END AS start_time,
    CASE WHEN dbo.table1.ACTIONID  = 2 
        THEN dbo.table1.startstop 
    END AS stop_time,
    dbo.table2.collect_time
FROM dbo.table2
JOIN dbo.table1 ON dbo.table1.CREATETIME = dbo.table2.CREATETIME;

...这给了我一个包含几行的结果表，每行都是重复的，一次开始-一次结束-时间（sql时间-为简单起见而缩短）-另一个为NULL-例如：

device | create_time | start_time | stop_time | collect_time
1      | 0000001     | 0000001    | NULL      | 0000001
1      | 0000001     | NULL       | 0000002   | 0000001

我想将这两行（以 create_time 作为 ID）分组，以便将它们合二为一......谢谢！

Answer 1

您可以聚合 (SUM) 这些列：

SELECT dbo.table2.device, 
    dbo.table2.CREATETIME AS create_time,
    SUM(CASE WHEN dbo.table1.ACTIONID = 1 
        THEN dbo.table1.startstop ELSE 0
    END) AS start_time,
    SUM(CASE WHEN dbo.table1.ACTIONID  = 2 
        THEN dbo.table1.startstop ELSE 0
    END) AS stop_time,
    dbo.table2.collect_time
FROM dbo.table2
JOIN dbo.table1 ON dbo.table1.CREATETIME = dbo.table2.CREATETIME
GROUP BY dbo.table2.device, dbo.table2.CREATETIME, dbo.table2.collect_time;

Answer 2

我也认为使用子查询也可以解决

SELECT
X.Device
,sum(X.start_time)
,sum(X.stop_time)
,X.collect_time
from(
SELECT dbo.table2.device, 
    dbo.table2.CREATETIME AS create_time,
    CASE WHEN dbo.table1.ACTIONID = 1 
        THEN dbo.table1.startstop 
    END AS start_time,
    CASE WHEN dbo.table1.ACTIONID  = 2 
        THEN dbo.table1.startstop 
    END AS stop_time,
    dbo.table2.collect_time
FROM dbo.table2
JOIN dbo.table1 ON dbo.table1.CREATETIME = dbo.table2.CREATETIME) AS X
group by
X.Device, X.collect_time