Re: how to do this join ?

juerg(dot)rietmann(at)pup(dot)ch writes:
> select *,
> (select a_typ from auftrag where a_nr=z_a_nr) as typ,
> (select a_t_definition_d from auftrags_typ where a_t_code=typ) as text
> from zylinder

Seems like a very non-SQLish way to proceed. Instead use joins:

select zylinder.*, a_typ as typ, a_t_definition_d as text
from zylinder, auftrag, auftrags_typ
where a_nr = z_a_nr and a_t_code = a_typ

If there were multiple matches in auftrag or auftrags_typ then this
would yield multiple rows per zylinder row, which you might not want;
but your subselect-based approach is already assuming there are not
multiple matches.

If there's a possibility of *no* matching row, then the first solution
would emit NULLs for the missing auftrag and auftrag_typ values, whereas
the second would emit nothing at all for that zylinder row. If that's
not what you want, you need to use outer joins (new in 7.1):

select zylinder.*, a_typ as typ, a_t_definition_d as text
from (zylinder left join auftrag on (a_nr = z_a_nr))
left join auftrags_typ on (a_t_code = a_typ);

regards, tom lane