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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