如果根据另一列中的值计算总和

Question

在下面的代码中，我希望AdminDuration和BreakDuration根据UserID的值进行求和。目前我无法弄清楚，并且它将所有持续时间的值与ReasonCode 7相加。结果，每个UserId的持续时间相同（不是我想要的！）。

Select SkillTargetID AS UserID, 
(SELECT sum(Duration) 
    from [t_Agent_Event_Detail] 
    where ReasonCode = 7 
    and DateTime > convert(DATETIME, '2013-01-31 08:00', 21)) as AdminDuration, 
(SELECT sum(Duration) 
    from [t_Agent_Event_Detail] 
    where ReasonCode = 6 
    and DateTime > convert(DATETIME, '2013-01-31 08:00', 21) 
    and SkillTargetID = [t_Agent_Event_Detail].SkillTargetID) as BreakDuration 
from [t_Agent_Event_Detail] 
GROUP BY SkillTargetID 

Answer 1

如果我理解正确的话，它应该是：

SELECT SkillTargetID AS UserID, 
     sum(CASE WHEN ReasonCode = 7 THEN Duration ELSE 0 END) as AdminDuration, 
     sum(CASE WHEN ReasonCode = 6 THEN Duration ELSE 0 END) as BreakDuration 
FROM [t_Agent_Event_Detail] 
WHERE DateTime > convert(DATETIME, '2013-01-31 08:00', 21) 
GROUP BY SkillTargetID