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Query composite index range in an efficient way

From: Havasvölgyi Ottó <havasvolgyi(dot)otto(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Query composite index range in an efficient way
Date: 2009-02-17 12:44:48
Message-ID: 34608c0c0902170444v7ac09d97h5ad971baa1dee673@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

Let's say I have a table (tbl) with two columns: id1, id2.
I have an index on (id1,id2)
And I would like to query the (12;34) - (56;78) range (so it also may
contain (12;58), (13;10), (40;80) etc.). With the index this can be done
quite efficiently in theory, but I cannot find a way to make this happen. I
triy this in the WHERE clause:

WHERE (id1>12 or id1=12 and id2>=34) and (id1<56 or id1=56 and id2<=78)

I created a big enough table (131072 records, and it had also a 3rd field
with about 120 character text data).
But Postgres performs a SeqScan. I have analyzed the table before it.
I also tried Row constructors with a Between expression, but in this case
Postgres handled the elements of the row independently, and this led to
false query result.

What should I write in the Where clause to get Postgres to perform an
IndexScan?

I would like to apply this to other datatypes also, not just ints.

Thanks in advance,
Otto

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Next:From: Matthew WakelingDate: 2009-02-17 12:56:54
Subject: Re: Query composite index range in an efficient way
Previous:From: Matthew WakelingDate: 2009-02-17 11:45:43
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