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https://issues.apache.org/jira/browse/CALCITE-3760?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17027518#comment-17027518
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Jin Xing commented on CALCITE-3760:
-----------------------------------
{quote}As we discussed recently, it would be illegal to merge those Projects
because of the UDF.
{quote}
Yes, in addition to rewriting SqlNode, determinism of operator also affects
plan optimization. I think that's CALCITE-2348 try to fix. Firing certain
rules on non-deterministic operators as normal might fail to guarantee plan
equivalence.
> Rewriting non-deterministic function can break query semantics
> --------------------------------------------------------------
>
> Key: CALCITE-3760
> URL: https://issues.apache.org/jira/browse/CALCITE-3760
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Jin Xing
> Assignee: Jin Xing
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> Calcite rewrite some *SqlFunctions* during validation. But whether the
> function is deterministic is not considered. For a non-deterministic
> operator, the rewriting can break semantics. Additionally there's no
> interface for user to specify the determinism for a UDF/UDAF.
> Say I have non-deterministic UDF & UDAF and run sql like below
> {code:java}
> select coalesce(udf(col0), 100) from foo;
> select nullif(udaf(col0), 1024) from foo;{code}
> They will be rewritten as
> {code:java}
> select case when udf(col0) is not null then udf(col0) else 100 end
> from foo;
> select case when udaf(col0)=1024 then null udaf(col0)
> from foo{code}
> As we can see that non-deterministic UDF & UDAF are called multiple times
> after written. Thus the condition in WHEN clause might NOT be held all the
> time.
> We need to provide an interface for user to specify the determinism in
> UDF/UDAF and consider whether a SqlNode is deterministic when rewriting.
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