Thanks a lot. pozdrowienia mk
2009/7/10 Pavel Stehule <pavel.steh...@gmail.com> > 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...@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 > > >
