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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-4651) Hidden assumptions in FromVTI.makeRestriction()
Date Tue, 11 May 2010 11:56:42 GMT
Hidden assumptions in FromVTI.makeRestriction()

                 Key: DERBY-4651
                 URL: https://issues.apache.org/jira/browse/DERBY-4651
             Project: Derby
          Issue Type: Bug
          Components: SQL
    Affects Versions:
            Reporter: Knut Anders Hatlen
            Priority: Minor

FromVTI.makeRestriction() has this code to strip away Boolean constants from AND and OR expressions:

            // strip off trailing vacuous constant if present
            if ( andOperator.getRightOperand() instanceof BooleanConstantNode )
            { return makeRestriction( andOperator.getLeftOperand(), columnNameMap ); }


            // strip off trailing vacuous constant if present
            if ( orOperator.getRightOperand() instanceof BooleanConstantNode )
            { return makeRestriction( orOperator.getLeftOperand(), columnNameMap ); }

The code for AND will only work as expected if the right operand is TRUE. The code for OR
only works correctly if the right operand is FALSE.

I'm not sure if this can ever result in user-visible bugs, since Boolean constants are usually
removed before we get to this point in the code. The predicate has probably been transformed
to conjunctive normal form, in which Boolean constants in the right operand of an AndNode
or an OrNode in fact is always TRUE or FALSE, respectively.

I think this code either should be changed to work regardless of the value of the constant
in the right operand, or the assumption that the predicate is on conjunctive normal form should
be documented in the comments (and perhaps also checked in an assert statement).

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