extend "group by" to include "empty relations" ?
I've two tables related via a id-field.
Table "public.fn_kat"
Column | Type |
-----------------+-----------------------------+-
id | integer |
kategorie | text |
Table "public.fn_dokumente"
Column | Type |
-----------------+-----------------------------+-
kategorie | integer |
content | text |
I now want to list all entries in table fn_kat and count the number of
entries in fn_dokumente that have the actual id.
# select k.kategorie,count(d.oid) from fn_kat k,fn_dokumente d where
k.id=d.kategorie group by k.kategorie;
kategorie | count
------------------------------------------+-------
1. Forschungsnetzwerk Erwachsenenbildung | 1
1.1. Protokolle | 3
2. Sonstige Dokumente | 1
But there is a problem now: There are also entries in fn_kat which dont
have corresponding entries in fn_dokumente and this entries should be
listed too. With the proper count=0 !!
How to achieve this?
thnx a lot,
peter
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peter pilsl wrote:
But there is a problem now: There are also entries in fn_kat which dont
have corresponding entries in fn_dokumente and this entries should be
listed too. With the proper count=0 !!
Your problem is not on the GROUP BY, but rather that you need an outer
join. Try something like
select k.kategorie,count(d.oid) from fn_kat k left join fn_dokumente d
on k.id=d.kategorie group by k.kategorie;
--
Alvaro Herrera http://www.PlanetPostgreSQL.org/
"The first of April is the day we remember what we are
the other 364 days of the year" (Mark Twain)
peter pilsl <pilsl@goldfisch.at> writes:
But there is a problem now: There are also entries in fn_kat which dont
have corresponding entries in fn_dokumente and this entries should be
listed too. With the proper count=0 !!
How to achieve this?
LEFT JOIN before the group by?
regards, tom lane