On Mon, Oct 24, 2011 at 5:46 PM, Joel Stevenson <jsteven...@bepress.com> wrote: > Hi all, I'm trying to enumerate a list of months between a date in the past > and now and display a value from an existing table if there is one for the > date or NULL if there isn't. > > I'm using this SQL to generate the months: > > select distinct date_trunc( 'month', '2011-06-01'::date + tally_day )::date > as tally_mon > from generate_series( 0, ( select current_date - '2011-06-01'::date ) ) as > tally_day > > [[ produces ]] > tally_mon > ------------ > 2011-06-01 > 2011-07-01 > 2011-08-01 > 2011-09-01 > 2011-10-01 > (5 rows) > > and I am trying to use it as the left hand side of a left join against my > data table: > > select tally_table. tally_mon, met.datum > from ( > select distinct date_trunc( 'month', '2011-06-01'::date + tally_day )::date > as tally_mon > from generate_series( 0, ( select current_date - '2011-06-01'::date ) ) as > tally_day > ) as tally_table full outer join my_existing_table as met on( tally_mon = > met.month ) > where met.series = 1; > -- ** See SETUP below ** > > This produces rows only for those that exist in my_existing_table and no left > join output which I'd expect for the rest of the tally_table rows. > > What am I missing? > > Many thanks, > Joel > > SETUP: > create temp table my_existing_table ( month date not null, series int not > null, datum int not null ); > insert into my_existing_table values ( '2011-08-01', 1, 5 ), ( '2011-10-01', > 1, 4 );
UNION ALL should do it for you. Something along these lines should work select tally_mon as mon, max(datum) as datum from ( select distinct date_trunc( 'month', '2011-06-01'::date + tally_day )::date as tally_mon,0 as datum from generate_series( 0, ( select current_date - '2011-06-01'::date ) ) as tally_day union all select month as tally_mon,datum from my_existing_table ) as tally_table group by mon order by 1 -- Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-sql
