如何从两个表的联合中选择最大日期？

Question

SELECT TOP 1 * FROM 
(
    select max(updatedtimestamp) from db1.dbo.policyrepresentationcache with(nolock)
    UNION
    select max(updatedtimestamp) from db2.dbo.policyrepresentationcache with(nolock)
    ) 
ORDER BY updatedtimestamp

我在这里遇到语法错误，我不确定如何设置它。

Answer 1

您只是缺少由联合产生的表的别名。 我别名它作为下方。

SELECT TOP 1 a.updatedtimestamp FROM
(
     select max(updatedtimestamp) as updatedtimestamp  
     from db1.dbo.policyrepresentationcache with(nolock)
     UNION
     select max(updatedtimestamp) 
     from db2.dbo.policyrepresentationcache with(nolock)
) a
ORDER BY a.updatedtimestamp

Answer 2

SELECT TOP 1 Temp.* FROM 
(
    select max(updatedtimestamp) from db1.dbo.policyrepresentationcache with(nolock)
    UNION
    select max(updatedtimestamp) from db2.dbo.policyrepresentationcache with(nolock)
    ) AS Temp
ORDER BY Temp.updatedtimestamp