Question : UNION and NOT EXISTS

i have two queries

ie:
select id from tableA where condition=true
select id from tableB where condition=true

if records are returned from the first query is there anyway to exclude records returned from the secord query. Please note that I know I can do a UNION and "NOT EXISTS" SUBQUERY on the secord query to restrict returned results, however I am hoping there is a better way as the second query is quite complicated and zaps the processor when run twice.

ie:
select id from tableA where condition=true
UNION
select id from tableB where condition=true and not exists (select id from tableA where condition=true)

thanks in advance.

Answer : UNION and NOT EXISTS

ooops forgot the TABLE keyword:

declare @tA table ( id int )
declare @tB table ( id int )
insert into @tA select id from tableA where condition=true
insert into @tB select id from tableB where condition=true
delete @tB where id in ( select id from @tA)
select * from @tA
union all
select * from @tB