Hallo Gunnar,
>
> SELECT
> mzb.land,
> count ( distinct (mzb.samplsite_id))
> FROM
> public.mzb
> WHERE
> EXTRACT (year from mzb.date) = 1999 AND
> EXTRACT (year from mzb.date) = 2000 AND
> EXTRACT (year from mzb.date) = 2001 AND
> EXTRACT (year from mzb.date) = 2002
> GROUP BY mzb.land;
>
OR statt AND?
oder IN (1999, 2000, 2001, 2002)
oder BETWEEN 1999 AND 2002
Gruß
Bernhard