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https://issues.apache.org/jira/browse/CALCITE-3746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17038244#comment-17038244
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Chunwei Lei commented on CALCITE-3746:
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{quote}why don't you add the metadata to your user-defined-functions instead?
If you add the metadata, then Calcite would never call the function with null
arguments, and it would enable Calcite to optimize the queries better.
For example, can you declare the function as a strict one? That would tell
Calcite the function always returns null if any of the arguments is null.
{quote}
You are assuming that every execution engine has such annotation and all udfs
should return null or other same value. What should I do if I want a udf which
returns 0 while another udf returns -1 when meeting NULL?
{quote}Note: RexSimplify code is huge. It deals with lots of things, and I
don't see a way of adding an option that would treat `is not null` in every
possible case.
Then I don't even get what you mean by "retain order" because predicates might
float all over the place. There is no order. RexSimplify might infer the
predicates, etc, etc
{quote}
Even though RexSimplify might infer the predicates, it doesn't change the order
for other operators, except IS NOT NULL and NOT. For instance, it doesn't
change {{a>1 and b<1}} to {{b<1 and a>1}}. What [~pzw2018]'s pr does is to
retain order for IS NOT NULL. Why should we always put {{IS NOT NULL}} at the
end?
> RexSimplify changes the order of IS NOT NULL in And RexNode
> -----------------------------------------------------------
>
> Key: CALCITE-3746
> URL: https://issues.apache.org/jira/browse/CALCITE-3746
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.20.0
> Reporter: pengzhiwei
> Assignee: Chunwei Lei
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> The RexSimplify changes the order of IS NOT NULL in And RexNode.The following
> expression
> {code:java}
> a is not null and length(a) > 0{code}
> is optimazted to
> {code:java}
> length(a) > 0 and a is not null{code}
> which will affect the logic short circuit for null-test.
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