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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4651) Hidden assumptions in FromVTI.makeRestriction()
Date Tue, 11 May 2010 16:12:41 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4651?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12866194#action_12866194
] 

Knut Anders Hatlen commented on DERBY-4651:
-------------------------------------------

In the OR case, I think the end result would actually end up being wrong. If the predicate
is X < 5 OR TRUE, and only X < 5 is pushed into the table function, the rows where X
>= 5 won't be returned from the table function and Derby has no way to recreate these outside
the table function.

But I agree, the predicates should have been normalized before we get there, so updating the
comments would probably suffice.

> 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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