Spatial query on large table with multiple self joins performing slow

Question

I am working on queries on a large table in Postgres 9.3.9. It is a spatial dataset and it is spatially indexed. Say, I have need to find 3 types of objects: A, B and C. The

Answer 1

Try this with inner join syntax and compare the results, there should be no duplicates. My guess is it should take 1/3rd the time or better than the original query :

select a.id as a_id, a.name as a_name, a.geog as a_geo,
       b.id as b_id, b.name as b_name, b.geog as b_geo,
       c.id as c_id, c.name as c_name, c.geog as c_geo
from table1 as a
INNER JOIN table1 as b on b.type='B'
INNER JOIN table1 as c on c.type='C'
WHERE a.type='A' and
     (ST_DWithin(a.geo, b.geo, 100) and ST_DWithin(a.geo, c.geo, 100))