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https://issues.apache.org/jira/browse/CALCITE-6453?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17862703#comment-17862703
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Krisztian Kasa commented on CALCITE-6453:
-----------------------------------------
Hi [~nobigo],
Thanks for the review.
I bumped into this when I was searching for the cause of a StackOverflow in the
Hive compiler running this query:
[https://github.com/apache/hive/blob/b15ce9126dcc596c953fe202e6834cebdfca6080/ql/src/test/queries/clientpositive/cardinality_preserving_join_opt2.q#L81-L92]
using Calcite 1.33.0
The predicate
{code:java}
(cm.c5 is null or cm.c5 > date_format(cast('2020-10-30' as date),'yyyy-MM-01'))
{code}
is represented as
{code:java}
OR(IS NULL($4), >($4,
CAST(date_format(CAST(_UTF-16LE'2020-10-30':VARCHAR(2147483647) CHARACTER SET
"UTF-16LE"):DATE, _UTF-16LE'yyyy-MM-01':VARCHAR(2147483647) CHARACTER SET
"UTF-16LE")):DATE))
{code}
The first RexSimplify.simplify() call transforms it to
{code:java}
OR(IS NULL($4), >($4, CAST(date_format(CAST(2020-10-30:DATE):DATE,
_UTF-16LE'yyyy-MM-01':VARCHAR(2147483647) CHARACTER SET "UTF-16LE")):DATE))
{code}
The second call simplifies it further to
{code:java}
OR(IS NULL($4), >($4,
CAST(date_format(2020-10-30:DATE,_UTF-16LE'yyyy-MM-01':VARCHAR(2147483647)
CHARACTER SET "UTF-16LE")):DATE))
{code}
The goal of this jira is to do the simplification in one step and end up with
an expression which can not be simplified further with subsequent simplify
calls.
> Simplify casts which are result of constant reduction
> -----------------------------------------------------
>
> Key: CALCITE-6453
> URL: https://issues.apache.org/jira/browse/CALCITE-6453
> Project: Calcite
> Issue Type: Improvement
> Reporter: Krisztian Kasa
> Assignee: Krisztian Kasa
> Priority: Major
> Labels: pull-request-available
>
> RexSimplify transforms nullable cast expressions with a non-nullable literal
> operand which type is different from the cast type to another cast expression
> with a literal operand with the same type as the cast.
> If simplify is called again using the result cast expression of the first
> simplification we get a literal only as a result.
> Example:
> Initial expression
> {code:java}
> CAST(_UTF-16LE'2020-10-30':VARCHAR(2147483647) CHARACTER SET "UTF-16LE"):DATE
> {code}
> where the operand is non-nullable varchar and the result of the cast is
> nullable date.
> After the first simplify call we get
> {code:java}
> CAST(2020-10-30:DATE):DATE
> {code}
> where the operand type is non-nullable date and the cast type is nullable
> date.
> https://github.com/apache/calcite/blob/8ab0b03326730aa2cc6b476b2cbd8f99799bdacb/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L2269-L2276
> After the second simplify call we get
> {code:java}
> 2020-10-30:DATE
> {code}
> where the literal type is non-nullable date
> https://github.com/apache/calcite/blob/8ab0b03326730aa2cc6b476b2cbd8f99799bdacb/core/src/main/java/org/apache/calcite/rex/RexSimplify.java#L2195-L2196
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