SQL 服务器排序依据与子查询中的最大行数

Question

以下查询适用于 PostgreSQL，我想知道为什么它不适用于 SQL Server 2016。

select * from (values (1),(2)) as a(a)
UNION
(
  select * from (values (1),(2)) as a(a)
  order by 1 desc
  offset 0 rows fetch first 1 rows only
)
order by 1 desc offset 0 rows fetch first 1 rows only

谁能给我解释一下为什么这里不支持 order by？

有趣的是，下面的另一种表达方式非常有效

select * from (values (1),(2)) as a(a)
where a.a in(
  select * from (values (1),(2)) as a(a)
  order by 1 desc
    offset 0 rows fetch first 1 rows only
)
order by 1 desc offset 0 rows fetch first 1 rows only

这是一个错误吗？

Answer 1

联合后的查询需要呈现为select，像这样：

select * from (values (1),(2)) as a(a)
UNION
select * from
(
select * from (values (1),(2)) as a(a)
order by 1 desc
offset 0 rows fetch first 1 rows only
) b
order by 1 desc offset 0 rows fetch first 1 rows only

SQL 服务器排序依据与子查询中的最大行数

SQL Server order by with max rows in subquery

sql

sql-server

sql-server-2016