From: | "Jim C(dot) Nasby" <jim(at)nasby(dot)net> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Partial index where clause not filtering through |
Date: | 2003-06-16 05:31:18 |
Message-ID: | 20030616003118.S66185@flake.decibel.org |
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Thread: | |
Lists: | pgsql-performance |
I have the following index:
street_range__street_locality_high_low_v btree (street_name_id,
locality_id, addr_high_v, addr_low_v) WHERE (addr_high_v IS NOT NULL)
The query has a where clause like this:
FROM street_range s, input i
WHERE 1=1
AND i.address_v IS NOT NULL
AND s.locality_id = i.locality_id
AND s.street_name_id = i.street_name_id
AND s.addr_low_v <= i.address_v
AND s.addr_high_v >= i.address_v
As-is, it won't use the index. i.address_v IS NOT NULL AND s.addr_high_v
>= i.address_v should mandate that s.addr_high_v must be not-null, if
I'm remembering how nulls work correctly. (Actually, having any kind of
comparison on s.addr_high_v should mandate NOT NULL since NULL != NULL,
right?) Therefore the optimizer should be able to deduce that it can use
the index.
Adding AND s.addr_high_v IS NOT NULL to the where clause makes
everything work fine, so there is a work-around. Just seems like a minor
item to add to the TODO.
--
Jim C. Nasby (aka Decibel!) jim(at)nasby(dot)net
Member: Triangle Fraternity, Sports Car Club of America
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