sql - 在 SQL Server 中结合 ORDER BY 和 UNION

Question

如何在一个结果集中获取表的第一条记录和表的最后一条记录？

此查询失败

SELECT TOP 1 Id,Name FROM Locations ORDER BY Id
UNION ALL
SELECT TOP 1 Id,Name FROM Locations ORDER BY Id DESC

有什么帮助吗？

Answer 1

将您的order byandtop语句放入子查询中：

select first.Id, first.Name 
from (
    select top 1 * 
    from Locations 
    order by Id) first
union all
select last.Id, last.Name 
from (
    select top 1 * 
    from Locations 
    order by Id desc) last

Answer 2

如果您使用的是 SQL Server 2005 或更高版本：

; WITH NumberedRows as (
    SELECT Id,Name,
       ROW_NUMBER() OVER (ORDER BY Id) as rnAsc,
       ROW_NUMBER() OVER (ORDER BY Id desc) as rnDesc
    FROM
        Locations
)
select * from NumberedRows where rnAsc = 1 or rnDesc = 1

唯一与您的原始查询不同的地方是表中只有一行（在这种情况下，我的答案返回一行，而您的答案将返回同一行两次）

Answer 3

select * from (
SELECT TOP 1 Id,Name FROM Locations ORDER BY Id) X
UNION ALL
SELECT TOP 1 Id,Name FROM Locations ORDER BY Id DESC

Answer 4

SELECT TOP 1 Id as sameColumn,Name FROM Locations 
UNION ALL
SELECT TOP 1 Id as sameColumn,Name FROM Locations ORDER BY sameColumn DESC