用于从多个表增加多个 case 函数的 SQL 语句

Question

我试图通过制作 1 个 case 语句来增加 SQL 生成的列“Counter”。 我在案例声明中收到计数器的错误“无效列”。如有任何帮助，我们将不胜感激。

SELECT 0 as Counter(Not part of any table),
CASE
          WHEN dateadd(HOUR, -1,GETDATE()) >= max (a.UPDATED_DATE)
          THEN
             Counter + 1 
WHEN dateadd(HOUR, -1,GETDATE()) >= max (b.UPDATED_DATE)
          THEN
             Counter + 1          
          ELSE
             Counter + 0
       END  as Counter
FROM dbo.My_Dates a, Client_Dates b

Answer 1

在黑暗中拍摄。目前尚不清楚您需要按什么顺序对行进行计数，也不清楚两个表之间的关系是什么。

with m as (
    SELECT *,
        case when max(a.UPDATED_DATE) over () >    max(b.UPDATED_DATE) over ()
             then max(a.UPDATED_DATE) over () else max(b.UPDATED_DATE) over () end as last_update
    FROM dbo.My_Dates a, Client_Dates b /* this cross join surely isn't right */
)
select
    count(case when dateadd(hour, -1, getdate()) >= last_update then 1 end)
        over (order by ??)
from m;

根据下面的评论，您似乎只需要计算一堆表中的最大值:

with d(last_updated) as (
    select max(UPDATED_DATE) from T1  union all
    select max(UPDATED_DATE) from T2  union all ...
    select max(UPDATED_DATE) from T16
)
select count(case when dateadd(hour, -1, getdate()) >= last_update then 1 end) from d;