"cristivoinicaru" <cristivoinicaru@dmhi.ct.ro> writes:
> I want like sql interogation to select only one record from each "gc" group
> record (who has the same code "gc" (that means that the "gc" field will be
> unique key)) with the following two condition:
> 1)from each "gc" group of records to select the record who has the value of
> "ora" field maxim.
> 2)if two ore more record have the same value of the maxim value of the "ora"
> to select oly one of them
I don't think you can do (2) very nicely in standard SQL, because the
results aren't fully defined and the SQL standard does not like poorly
defined behaviors ;-). However there is a nonstandard extension in
Postgres that is exactly what you need: SELECT DISTINCT ON. See the
"weather reports" example in the SELECT reference page --- your "gc"
corresponds to weather stations and "ora" to report date.
regards, tom lane
