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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