UNION 查询时 为何不是第一个表的数据排在前面 在线等

[yiyezhiqiu]

select a1,a2,a3 from a
union
select b1,b2,b3 from b

查询结果 是 a表中的数据和b表中的数据混合着 ，没有指定任何排序，有什么办法指定 结果是 a表中的数据排在前面，表b中的数据库排在后面

[OracleRoob]

select *
from (
select a1,a2,a3,1 as xh from a
union
select b1,b2,b3,2 as xh from b ) T
order by xh

[qys2000]

select *
from (
select a1,a2,a3,1 as xh from a
union
select b1,b2,b3,2 as xh from b ) T
order by xh
这种方法可行！

[crazyflower]

ls正解。

[-狙击手-]

select a1,a2,a3 ,1 as id from a
union
select b1,b2,b3,2 from b
order by id

[yiyezhiqiu]

这个方法 能达到 我需要的结果 ，可是会导致 不能去掉两个表中的重复行

[OracleRoob]

--可以合并重复行。

select *
from (
select a1 as f1,a2 as f2,a3 as f3,1 as xh from a
union
select b1 as f1,b2 as f2,b3 as f3,2 as xh from b) T1
where checksum(f1,f2,f3) in
(select checksum(*)
from
(
select a1 as f1,a2 as f2,a3 as f3 from a
union
select b1 as f1,b2 as f2,b3 as f3 from b
) as T2)
order by xh

[yiyezhiqiu]

谢谢各位