LEFT JOIN ...

Morning ...

I'm trying to wrack my brain over something here, and no matter
how I try and look at it, I'm drawing a blank ...

I have two tables that are dependent on each other:

notes (86736 tuples) and note_links (173473 tuples)

The relationship is that one note can have several 'ppl' link'd to
it ...

I have a third table: calendar (11014 tuples) ... those calendar
entries link to a note.

So you have something like:

personA ---
personB --|--> note_links --> notes --[maybe]--> calendar entry
personC ---

now, the query I'm workign with is:

SELECT n.note, n.nid, n.type, c.act_type, c.status, nl.contact_lvl,
CASE WHEN c.act_start IS NULL
THEN date_part('epoch', n.added)
ELSE date_part('epoch', c.act_start)
END AS start
FROM note_links nl, notes n LEFT JOIN calendar c ON (n.nid = c.nid)
WHERE (n.type = 'A' OR n.type = 'N' OR n.type = 'H' OR n.type = 'C')
AND (nl.id = 15748 AND contact_lvl = 'company')
AND n.nid = nl.nid
ORDER BY start DESC;

Which explains out as:

NOTICE: QUERY PLAN:

Sort (cost=7446.32..7446.32 rows=1 width=88)
-> Nested Loop (cost=306.52..7446.31 rows=1 width=88)
-> Index Scan using note_links_id on note_links nl (cost=0.00..3.49 rows=1 width=16)
-> Materialize (cost=6692.63..6692.63 rows=60015 width=72)
-> Hash Join (cost=306.52..6692.63 rows=60015 width=72)
-> Seq Scan on notes n (cost=0.00..2903.98 rows=60015 width=36)
-> Hash (cost=206.22..206.22 rows=10122 width=36)
-> Seq Scan on calendar c (cost=0.00..206.22 rows=10122 width=36)

EXPLAIN

and takes forever to run ...

Now, if I eliminate the LEFT JOIN part of the above, *one* tuple is
returned ... so even with the LEFT JOIN, only *one* tuple is going to be
returned ...

Is there some way to write the above so that it evaluates:

WHERE (n.type = 'A' OR n.type = 'N' OR n.type = 'H' OR n.type = 'C')
AND (nl.id = 15748 AND contact_lvl = 'company')
AND n.nid = nl.nid

first, so that it only has to do the LEFT JOIN on the *one* n.nid that is
returned, instead of the 86736 that are in the table?

Marc G. Fournier ICQ#7615664 IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy(at)hub(dot)org secondary: scrappy(at){freebsd|postgresql}.org