Question

我想选择state或workstate列。首选是首先使用state值。如果它为null或为空，那么我想使用workstate值。

我有以下sql：

SELECT        
COUNT(id) AS participants, 

COALESCE(NULLIF(state,''), workState, (select state from dbo.training where id =(SELECT top(1) trainingId
    FROM dbo.Xref_Participant_Training
    WHERE (participantId = dbo.Participant.id) )) ) as state

FROM dbo.Participant
WHERE EXISTS
    (SELECT 1
        FROM dbo.Xref_Participant_Training
        WHERE (participantId = dbo.Participant.id) AND (dbo.Participant.country = 'United States'))
GROUP by COALESCE(NULLIF(state,''), workState, (select state from dbo.training where id =(SELECT top(1) trainingId
        FROM dbo.Xref_Participant_Training
        WHERE (participantId = dbo.Participant.id) )) )

我收到以下错误：

Msg 144, Level 15, State 1, Line 15
Cannot use an aggregate or a subquery in an expression used for the group by list of a GROUP BY clause.

Answer 1

这是对原始问题的回答。

问题是您需要将整个表达式放在group by：

中

SELECT COUNT(id) AS participants, 
       COALESCE(NULLIF(p.state,''), p.workState) as state
FROM dbo.Participant p
WHERE EXISTS (SELECT 1
              FROM dbo.Xref_Participant_Training pt
              WHERE pt.participantId = p.id
             ) AND
      p.country = 'United States'
GROUP BY COALESCE(NULLIF(p.state, ''), p.workState);

您的查询存在的问题是GROUP BY state实际上意味着GROUP BY p.state。但是，您希望按SELECT。

中定义的列进行汇总

另外：

表别名使查询更易于编写和阅读。
EXISTS子查询不需要列名。

Answer 2

更改GROUP BY以包含整个表达式

SELECT        
       COUNT(id) AS participants, 
       COALESCE(NULLIF(state,''), workState) as state
FROM   dbo.Participant
WHERE EXISTS
    (SELECT participantId
        FROM dbo.Xref_Participant_Training
        WHERE (participantId = dbo.Participant.id) AND (dbo.Participant.country = 'United States'))
GROUP BY COALESCE(NULLIF(state,''), workState)

对于更新的查询，当查询变得复杂时，使用派生表或cte

会更容易

派生表的示例语法

select col1, col2, count(*)
from
(
    select col1, col2 = coalesce(col2, col3), col4, col5
    from   sometable
) d
group by col1, col2

如果为null或为空，请选择其他列

2 个答案: