Thank's Svein Erling,

I would expect the same results from

> from materialart ma
> left outer join entsorgungskopf ek
> on ma.abfallschluessel = ek.abfallschluessel
> and ma.unterschluessel = ek.unterschluessel
> left outer join entsorgungsposition ep
> on ek.lfd_ent_kop_nr = ep.lfd_ent_kop_nr
> where
> ep.datum is null
> or ep.datum between '01.04.2006' and '19.04.2006'

and

> from materialart ma
> left outer join entsorgungskopf ek
> on ma.abfallschluessel = ek.abfallschluessel
> and ma.unterschluessel = ek.unterschluessel
> left outer join entsorgungsposition ep
> on ek.lfd_ent_kop_nr = ep.lfd_ent_kop_nr
> and ep.datum between '01.04.2006' and '19.04.2006'

But that's not right. It look's as if the reference to ep within the where
clause excludes those records without matches.

Thank You.
fr.