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Index usage when bitwise operator is used

From: "W(dot)Alphonse HAROUNY" <wharouny(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Index usage when bitwise operator is used
Date: 2007-09-13 12:30:20
Message-ID: f97d4e240709130530ve3cc522g61ccca23335618f4@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
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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