Question

select  first(orderid), accountid 
from [Order] 
group by AccountId 
order by DateCreated desc

first（）是无效的功能。

max（）不适用于唯一标识符

我如何获得为所有帐户创建的最后一个orderid？感谢。

Answer 1

像（未经测试）的东西：

;WITH CTE_LatestOrders AS (
    select accountid, lastcreated = max(datecreated)
    from [Order]
    group by accountid
)
select
    accountid, orderid
from
    [Orders] o
    join CTE_LatestOrders l 
        on o.AccountID = l.AccountID 
        and o.datecreated = l.lastcreated

Answer 2

您也可以在下面继续。

Select Temp.orderid, T.AccountId, T.DateCreated
From
(
    Select AccountId, max(DateCreated) as  DateCreated
    From [Order]
    Group By AccountId
)T
Inner Join [Order] Temp on Temp.AccountId = T.AccountId 
AND Temp.DateCreated = T.DateCreated

CTE不是UDT / temp表;将CTE视为仅针对当前查询定义的视图。就像一个视图一样，CTE被扩展并折叠成整体查询计划。全局优化仍将发生，但不要仅仅因为您使用CTE而只考虑执行一次查询。这是一个适合这个空间的简单示例：WITH vw AS（SELECT COUNT（*）c FROM Person）SELECT a.c，b.c FROM vw a，vw b;查询计划将清楚地显示两个扫描/聚合和连接，而不是仅两次投射相同的结果。

Answer 3

Max（）适用于MS SQL 2012中的唯一标识符

MS SQL问题：Max和GUID

3 个答案: