Answer of the question is wrong !!

select @@VERSION

create table #t1 (col int not null)

create table #t2 (col int not null)

create table #t3 (col int not null)

insert #t1 values (1), (1)

insert #t2 values (2)

insert #t3 values (3)

select COL from #t1

UNION

select COL from #t2

union all

select COL from #t3

select COL from #t1

UNION ALL

select COL from #t2

union all

select COL from #t3

Result:

Microsoft SQL Server 2008 R2 (RTM) - 10.50.1617.0 (X64) Apr 22 2011 19:23:43 Copyright (c) Microsoft Corporation Data Center Edition (64-bit) on Windows NT 6.1 <X64> (Build 7600: )

COL

1

2

3

COL

1

1

2

3