Sorry for not listing the exact layout of temp_XXXX:
obsdb=> \d temp_dry_at_2m
Table "public.temp_dry_at_2m"
Column | Type | Modifiers
----------------+-----------------------------+-----------
obshist_id | integer | not null
station_id | integer | not null
timeobs | timestamp without time zone | not null
temp_dry_at_2m | real | not null
Indexes:
"temp_dry_at_2m_pkey" primary key, btree (obshist_id)
"temp_dry_at_2m_idx" btree (station_id, timeobs)
The difference between the two queries is if a (station_id,timeobs) row is missing in one table, then the first returns one record(null,9.3) while the second return no records.
Regards,
Kim Bisgaard.
Tom Lane wrote:
Kim Bisgaard <kib+pg@dmi.dk> writes:
I have two BIG tables (virtually identical) with 3 NOT NULL columns
Station_id, TimeObs, Temp_XXXX, with indexes on (Station_id, TimeObs)
and valid ANALYSE (set statistics=100). I want to join the two tables
with a FULL OUTER JOIN.
I'm confused. If the columns are NOT NULL, why isn't this a valid
transformation of your original query?
select temp_max_60min,temp_dry_at_2m
from station s natural join
temp_dry_at_2m a full outer join temp_max_60min b using (station_id, timeobs)
where s.wmo_id=6065
and _a.timeobs='2004-1-1 0:0:0' and b._timeobs='2004-1-1 0:0:0'
and '2004-1-1 0:0:0' between s.startdate and s.enddate;
Seems like it's not eliminating any rows that would otherwise succeed.
regards, tom lane
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Kim Bisgaard
Computer Department Phone: +45 3915 7562 (direct)
Danish Meteorological Institute Fax: +45 3915 7460 (division)
