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https://issues.apache.org/jira/browse/CALCITE-1116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15180539#comment-15180539
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Julian Hyde commented on CALCITE-1116:
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In addition to (or perhaps instead of) the tests you added to RelOptRulesTest,
can you add tests to RexProgramTest.testSimplify? These tests are more specific
and easier to write and debug than RelOptRulesTest tests.
Can you review null semantics carefully? "a > 5" is not equivalent to "NOT(a <=
5)" when there are nulls involved. There's not an easy solution. Usually
boolean expressions have an implicit "... IS TRUE" so it doesn't matter, but
it's hard to be sure you're in that situation. NullSafeVisitor may help, by
making null semantics explicit; after NullSafeVisitor has made a pass, {{a}}
would be converted to {{CAST(a AS ... NOT NULL)}} and therefore you can see
that nulls are not in play.
Do the HashSets in simplifyAnd2 make the behavior non-deterministic? (How
ironic.) For instance, you iterate over notNullOperands. There's LinkedHashSet
but also consider using the humble ArrayList (it's cheap). I don't know whether
you expect to see term lists of a size where O(n) contains would be a problem.
Since RexNode doesn't override equals and hashCode maybe you should be building
sets of strings.
Your {{RexUtil.negate(RexCall)}} method does the same thing as
{{NullSafeVisitor.negate(RexCall call)}} that I just added. Can you please
combine. (Your negate method returns null in theory but not in practice. It
should stop being wimpy and just throw.)
Similarly, your {{RexUtil.invert}} method should leverage {{SqlKind.reverse}}
or {{RexImplicationChecker.InputUsageFinder.reverse}}.
On a couple of occasions you write {{termsSet.containsAll(new
HashSet(collection))}} where you could write
{{termsSet.containsAll(collection)}}.
> Extend simplify for reducing expressions
> ----------------------------------------
>
> Key: CALCITE-1116
> URL: https://issues.apache.org/jira/browse/CALCITE-1116
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Jesus Camacho Rodriguez
> Assignee: Jesus Camacho Rodriguez
>
> We would like to cover more cases in expression simplification, such as:
> x>5 and x is not null => x>5
> x>5 and x is null => not satisfiable
> x>5 and x<=5 => not satisfiable
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