Hello
you can do it simply in new PostgreSQL 8.4. In older version the best
way what I know is using a stored procedure, that returns table
create or replace function foo()
returns setof yourtablename as $$
declare r yourtablename; s yourtablename; result youratblename; first boolean = true;
begin for r in select * from yourtablename loop order by ... if first then return next r; s := r; first :=
false; else if r.a is distinct from s.a then result.a := r.a else result.a
:= NULL end if; if r.b is distinct from s.b then result.b := r.b else result.b
:= NULL end if; if r.c is distinct from s.c then result.c := r.c else result.c
:= NULL end if; if r.d is distinct from s.d then result.d := r.d else result.d
:= NULL end if; return next result; end if; s := r; end loop; return;
end;
$$ language plpgsql;
select * from foo();
regards
Pavel Stehule
2009/7/10 Marcin Krawczyk <jankes.mk@gmail.com>:
> Hi list,
>
> I was wondering if it was possible for a field in SQL query to return NULL
> if latter value is exactly the same ? - for given ORDER BY clause, I guess.
> For example, query returns:
>
> xxyy 1 4 true
> xxyy 5 7 true
> xxyy 21 8 true
> yyzz 5 1 false
> yyzz 7 7 false
> yyzz 8 34 false
>
> I'd like the output to be:
>
> xxyy 1 4 true
> NULL 5 7 NULL
> NULL 21 8 NULL
> yyzz 5 1 false
> NULL 7 7 NULL
> NULL 8 34 NULL
>
> Is there any magical trick to achieve this ?
>
> regards
> mk
>