> and how would I use DISTINCT ON for this query? Please bear in mind,
> that there is more then one id_bf (just stopped the sample data with
> one of them)
I posted the answer more than hour ago:
SELECT DISTINCT ON (id_rf) * FROM rfmitzeit ORDER BY id_rf,
letztespeicherung DESC;
The equivalent with window functions would be:
SELECT * FROM (SELECT *,row_number() OVER (PARTITION BY id_rf ORDER BY
letztespeicherung DESC) FROM rfmitzeit) t WHERE row_number=1
If you check the query plan you will understand why DISTINCT ON is the
best option. Essensially, DISTINCT ON has no additional cost other the
cost of
ORDER BY id_rf, letztespeicherung DESC
which is unavoidable