[jira] [Created] (CALCITE-3760) Rewriting function without considering determinism can break query semantics

["Jin Xing (Jira)" <ji...@apache.org>]

Jin Xing created CALCITE-3760:
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             Summary: Rewriting function without considering determinism 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


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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