Re: Retrieve most recent 1 record from joined table

agharta schrieb am 22.08.2014 um 10:05:
> Joining the tables, how to get ONLY most recent record per table3(t3_date)??
> 
> Query example:
> 
> select * from table1 as t1
> inner join table2 t2 on (t1.t1_id = t2.t1_id and t2.t2_value like('%ab%') )
> inner join table3 t3 on (t2.t2_id = t3.t2_id and t3.t3_date <= timestamp '2014-08-20')
> order by t3.t2_id, t3.t3_date desc
> 

This seems to be slightly faster, especially with the following index:
 create index idx_t3_combined on table3 (t2_id, t3_date desc, t3_id);

select *
from table1 as t1 join table2 t2 on t1.t1_id = t2.t1_id and t2.t2_value like '%ab%' join (    select distinct on
(t2_id)t3_id,            t3_date,           t2_id    from table3    order by t2_id, t3_date desc ) t3 on t3.t2_id =
t2.t2_id
 
order by t3.t2_id, t3.t3_date desc
;

I also had to increase the work_mem in order to avoid disk based sorting for the joins