如何SUM包含嵌套的select语句的case语句？

Question

这是我的初始查询：

select 
CASE WHEN a.TO_WG_ID is null 
and a.CREATED_DATE_TIME = 
(select min(b.created_date_time) from ymtn.message b 
where b.thread_id = a.thread_id) THEN 1 ELSE 0 
END AS "Created" 
from ymtn.MESSAGE a 
left join YMTN.WORKGROUP b 
ON a.FROM_WG_ID=b.WORKGROUP_ID 
where b.WORKGROUP_ID='1STOP_PROCESS' 

它给了我和一帮1' 和0的一列。我想要的只是总和......只是一个数字，例如1691.如果我把一个SUM放在case语句前，我得到这个错误： Msg 130，Level 15，State 1，Line 5 无法对包含聚集或子查询的表达式执行聚合函数。那我该怎么做呢？我已与此查询工作：

select count(CREATED_DATE_TIME) as 'Created' 
from ymtn.MESSAGE a 
LEFT JOIN YMTN.WORKGROUP b 
ON a.FROM_WG_ID=b.WORKGROUP_ID 
where CREATED_DATE_TIME=(SELECT MIN(b.CREATED_DATE_TIME) FROM YMTN.MESSAGE b WHERE 
b.THREAD_ID = a.THREAD_ID) 
and a.TO_WG_ID is null 
and b.WORKGROUP_ID='1STOP_PROCESS' 

但是我希望它在case语句工作，而不必移动嵌套选择到WHERE子句。

Answer 1

你可以把整个事情放入一个子查询中，然后求和？

select sum(Created) 
from (
    select 
    CASE WHEN a.TO_WG_ID is null 
    and a.CREATED_DATE_TIME = 
    (select min(b.created_date_time) from ymtn.message b 
    where b.thread_id = a.thread_id) THEN 1 ELSE 0 
    END AS "Created" 
    from ymtn.MESSAGE a 
    left join YMTN.WORKGROUP b 
    ON a.FROM_WG_ID=b.WORKGROUP_ID 
    where b.WORKGROUP_ID='1STOP_PROCESS' 
) a