Index usage in bitwise operation context

From: "W(dot)Alphonse HAROUNY" <wharouny(at)gmail(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: Index usage in bitwise operation context
Date: 2007-09-13 12:34:32
Message-ID: f97d4e240709130534h3464403esf08ab8be2d5bedbf@mail.gmail.com
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Hello,

My question is about index usage when bitwise operations are invoked.
Situation Context:
--------------------------

Lets suppose we have 2 tables TBL1 and TBL2 as the following:
TBL1 {
......... ;
integer categoryGroup; // categoryGroup is declared as an index on TABL1
......... ;
}

TBL2 {
......... ;
integer categoryGroup; // categoryGroup is declared as an index on TABL2
......... ;
}

By conception, I suppose that:
- [categoryGroup] may hold a limited number of values, less than 32 values.
- [categoryGroup] is of type integer => it means 4 bytes => 32 bits
=> 32 places available to hold binary '0' or binary '1' values.
- [categoryGroup] is the result of an "OR bitwise operation" among a
predefined set of variables [variableCategory].
We suppose that [variableCategory] is of type integer (=>32 bits)
and each binary value of [variableCategory] may only hold a single binary
'1'.

Ex: variableCategory1 = 00000000000000000000000000000010
variableCategory2 = 00000000000000000000000000100000
variableCategory3 = 00000000000000000000000000001000

If [categoryGroup] = variableCategory1 | variableCategory2 |
variableCategory3
=>[categoryGroup] = 00000000000000000000000000101010

Question:
--------------
I have an SQL request similar to:

SELECT ..... FROM TBL1, TBL2 WHERE
<inner join between TBL1 and TBL2 is True> AND
TBL1.CATEGORY & TBL2.CATEGORY <> 0 //-- where & is the AND bitwise
operator

Qst:
1/ IS the above SQL request will use the INDEX [categoryGroup] defined on
TBL1 and TBL2 ?
2/ What should I do or How should I modify my SQL request in order
to force the query engine to use an index ? (the already defined index or
another useful index)

Thx a lot

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