Question

我正在处理两个查询，这些查询从一个表中提取数据。我可以让它们按照自己的意愿运行，但是如果可能的话，我希望将它们组合成一个。我已经在[Multiple COUNT SELECTS from the same table in one query中尝试了该解决方案，但无法弄清楚。以下是我正在从事的工作：

--goback 30 days start at midnight
declare @daysgoingback as int
set @daysgoingback = 90

declare @olderdate as datetime
set @olderdate = DATEADD(Day, -@daysgoingback, DATEDIFF(Day, 0, GetDate()))

--today at 11:59pm
declare @today as datetime
set @today = dateadd(ms, -3, (dateadd(day, +1, convert(varchar, GETDATE(), 101))))
print @today

--these are the two queries I'd like to combine:
select 
    avg(x.LogAlerts*1.0 / @daysgoingback) as 'Avg number of log alerts'
from
    (select count(*) as LogAlerts 
     from message_log_table 
     where msg_timestamp between @olderdate and @today) X

select 
    avg(x.MessagesDeleted*1.0 / @daysgoingback) as 'Avg number of messages deleted'
from
    (select count(*) as MessagesDeleted 
     from message_log_table 
     where msg_details like '%message deleted%' 
       and msg_timestamp between @olderdate and @today) X

Answer 1

“ AVG”是一个聚合函数，用于平均多行。您的“ select count（*）”子查询总是返回恰好一行，因此您并未真正按预期使用AVG函数。

您可以像这样将两者结合起来：

   select   count(*) * 1.0 / @daysgoingback as 'Avg number of log alerts'
            , count(case when msg_details like '%message deleted%' then 1 end) * 1.0 / @daysgoingback as 'Avg number of messages deleted'
    from    message_log_table 
    where   msg_timestamp between @olderdate and @today;

Answer 2

将每个查询放入CTE，然后交叉联接。

两个查询都只返回一个单元格结果，因此这里不需要花哨。

SQL Server：在一个查询中来自同一表的多个选择语句

2 个答案: