SQL Server query with union and different order by to each section?

问题

I've searched here on the site. and there are many version of answers to this question. But couldn't find what I was looking for for this specific question :

lets say that xxx,yyy,zzz has 1 column, 3 rows:

1   
2   
3   

SELECT a FROM xxx  order by a asc
UNION 
SELECT f FROM yyy order by f desc
UNION 
SELECT t FROM zzz order by t asc

So the desired result set is:

1
2
3
3
2
1
1
2
3

There is an error of incorrect syntax near UNION.

I'm aware of the order problem with union (and know how to solve it only if an overall ORDER BY is required.)

Question :

how can I get my desired output?

回答1:

You have to apply a single order by clause to the entire union, or else the ordering isn't well defined:

SELECT a,1 as Pos,a as Ord from xxx
UNION ALL
SELECT f,2,-f from yyy
UNION ALL
SELECT t,3,t from zzz
ORDER BY Pos,Ord

However, the -f might feel like a dirty trick to achieve the opposite ordering (or may not be entirely what you want if NULLs are included), so you could also do:

SELECT a,1 as Pos,a as OrdAsc,0 as OrdDesc from xxx
UNION ALL
SELECT f,2,0,f from yyy
UNION ALL
SELECT t,3,t,0 from zzz
ORDER BY Pos asc,Ord asc,OrdDesc desc

---

I'm unclear on why you don't think it answers your question - perhaps because of the additional columns in the result set? If so, you can arrange for the whole UNION to be in a subquery:

create table #xxx (a int not null)
create table #yyy (f int not null)
create table #zzz (t int not null)
insert into #xxx (a) select 1 union all select 2 union all select 3
insert into #yyy (f) select 1 union all select 2 union all select 3
insert into #zzz (t) select 1 union all select 2 union all select 3

SELECT a FROM (
SELECT a,1 as Pos,a as Ord from #xxx
UNION ALL
SELECT f,2,-f from #yyy
UNION ALL
SELECT t,3,t from #zzz
) t
ORDER BY Pos,Ord

results:

a
----
1
2
3
3
2
1
1
2
3

回答2:

Things to keep in mind while UNIONing:

• UNION allows you to create a RESULTSETwith same type data from different SELECT statement.
• The RESULTSET is generated with the column name of leading(first) SELECT statement.
• For other SELECT statement columns data type should be matched according to the leading(first) SELECT statement.
• For ORDERing, its applied on the RESULTSET, consequently in case of UNION, it only allows ORDER BY at the last SELECT statement but takes column name according to leading(first) SELECT statement, so below example is true:
• Finally, since in the RESULTSET for UNIONing with different tables/sources aggregates all data into a column(according to first(leading) SELECT statement), so you can not apply ASC and DESC for same column.

Right

SELECT a FROM xxx 
UNION 
SELECT f FROM yyy
UNION 
SELECT t FROM zzz order by a asc

Wrong: according to you

SELECT a FROM xxx 
UNION 
SELECT f FROM yyy
UNION 
SELECT t FROM zzz order by a asc, a desc

来源：https://stackoverflow.com/questions/8457103/sql-server-query-with-union-and-different-order-by-to-each-section