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https://issues.apache.org/jira/browse/CALCITE-2615?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16646626#comment-16646626
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Zoltan Haindrich commented on CALCITE-2615:
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in 3 valued logic the following stands:
{code}
a and b can be any expressions
(a || b) = (a || ( (a is null || !a) && b) = (a || ( (a is not true) && b)
{code}
so my first fix was totally right...if we are able to simplify {{a is not
true}} to {{!a}} then we are back to the stronger predicate.
right now I'm not sure which one is better...both has some pros/cons:
* keeping the old
** pro: it can do simplifications deeper; because it relies on predicates
** con: it may miss some opportunities; because it relies on the order of the
predicates appearing
* new:
** pro: it can notice (a || !a) pairs more reliably - I think this could be
fixed for the old as well
** con: it doesn't support deeper simplification cases at all.
> When simplifying NOT-AND-OR, RexSimplify incorrectly applies predicates
> deduced for operands to the same operands
> -----------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-2615
> URL: https://issues.apache.org/jira/browse/CALCITE-2615
> Project: Calcite
> Issue Type: Task
> Reporter: Julian Hyde
> Assignee: Zoltan Haindrich
> Priority: Major
> Labels: newbie
>
> When simplifying NOT-AND-OR, RexSimplify incorrectly applies predicates
> deduced for operands to the same operands.
> Here is the test case (add it to RexProgramTest):
> {code:java}
> @Test public void testSimplifyNotAnd() {
> final RexNode e = not(
> and(
> gt(and(vBool(1), literal(true)),
> or(literal(true), literal(true), literal(false))),
> gt(isNotNull(vBool(0)), eq(literal(false), vBool(1))),
> or(ne(literal(true), literal(false)),
> ge(vInt(0), literal((Integer) null)))));
> final String expected = "TODO";
> checkSimplify(e, expected);
> }
> {code}
> When you run it, verify will find a combination of assignments such that the
> simplified expression returns a different result than the original.
> The test case is not minimal; sorry. Maybe it reproduces with NOT-OR.
> The bug is in
> [RexSimplify.simplifyAndTerms|https://github.com/apache/calcite/blob/6b3844c0634792263a5073b8ea93565fb3415f41/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L412].
> Put a breakpoint at that line to see the problem. It passes through the
> operands once, building a list of predicates. Then it passes through the
> operands again, simplifying each operand. Thus operand1 is simplified using a
> list of predicates that includes the predicate 'not operand1'. Clearly wrong.
> [~kgyrtkirk], I warned that this was possible in our discussions.
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