From: | andrew(at)pillette(dot)com |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | How to optimize a JOIN with BETWEEN? |
Date: | 2006-02-20 04:06:12 |
Message-ID: | 200602200406.k1K46CB09448@pillette.com |
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Lists: | pgsql-performance |
Here's a simplified version of the schema:
Table A has an ID field, an observation date, and other stuff. There are about 20K IDs and 3K observations per ID. Table B has a matching ID field, minimum and maximum dates, a code, and other stuff, about 0-50 records per ID. For a given ID, the dates in B never overlap. On A, the PK is (id, obsdate). On B, the PK is (id, mindate). I want
SELECT a.id, b.code, AVG(other stuff) FROM A LEFT JOIN B ON a.id=b.id AND a.obsdate BETWEEN b.mindate AND b.maxdate GROUP BY 1,2;
Is there a way to smarten the query to take advantage of the fact at most one record of B matches A? Also, I have a choice between using a LEFT JOIN or inserting dummy records into B to fill in the gaps in the covered dates, which would make exactly one matching record. Would this make a difference?
Thanks.
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