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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4651) Hidden assumptions in FromVTI.makeRestriction()
Date Tue, 11 May 2010 13:24:42 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866143#action_12866143
] 

Rick Hillegas commented on DERBY-4651:
--------------------------------------

Thanks for looking closely at the code, Knut. The improvement you suggest sounds like a good
idea, if only because the code is puzzling. I believe that the vacuous trailing constants
are added by the normalization logic and are always TRUE in the case of ANDs and FALSE in
the case of ORs. In any event, I don't think any rows will be incorrectly qualified. That
is because the qualification is redundantly enforced by Derby after the table function returns
each row.

> 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: 10.6.1.0
>            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 );
}
> and
>             // 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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