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https://issues.apache.org/jira/browse/CALCITE-7042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17955147#comment-17955147
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Alessandro Solimando commented on CALCITE-7042:
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[~xuzifu666], I have corrected a typo in the title ("id" -> "is"), please keep
it in mind for the final squash and commit message format, hth
> Eliminate nested TRIM calls, exploiting the fact that TRIM is idempotent
> ------------------------------------------------------------------------
>
> Key: CALCITE-7042
> URL: https://issues.apache.org/jira/browse/CALCITE-7042
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Affects Versions: 1.39.0
> Reporter: Yu Xu
> Assignee: Yu Xu
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.41.0
>
>
> Trim function does not have idempotency simplification currently,
> trim(...trim(' aa ')) should be convert to trim(' aa ').
> sql:
> {code:java}
> select trim(trim(' aa ')); {code}
> plan:
> {code:java}
> EnumerableCalc(expr#0=[{inputs}], expr#1=[FLAG(BOTH)], expr#2=[' '],
> expr#3=[' aa '], expr#4=[TRIM($t1, $t2, $t3)], expr#5=[TRIM($t1, $t2, $t4)],
> EXPR$0=[$t5])
> EnumerableValues(tuples=[[{ 0 }]]){code}
> should convert to plan would be better:
> {code:java}
> EnumerableCalc(expr#0=[{inputs}], expr#1=[FLAG(BOTH)], expr#2=[' '],
> expr#3=[' aa '], expr#4=[TRIM($t1, $t2, $t3)], EXPR$0=[$t4])
> EnumerableValues(tuples=[[{ 0 }]]) {code}
>
> sql:
> {code:java}
> select trim(both 'c' from trim(both 'c' from ' aa ')); {code}
> should be:
> {code:java}
> select trim(both 'c' from ' aa '); {code}
> plan:
> {code:java}
> EnumerableCalc(expr#0=[{inputs}], expr#1=[FLAG(BOTH)], expr#2=[' '],
> expr#3=[' aa '], expr#4=[TRIM($t1, $t2, $t3)], expr#5=[TRIM($t1, $t2, $t4)],
> EXPR$0=[$t5])
> EnumerableValues(tuples=[[{ 0 }]]){code}
> should convert to plan would be better:
> {code:java}
> EnumerableCalc(expr#0=[{inputs}], expr#1=[FLAG(BOTH)], expr#2=['c'],
> expr#3=[' aa '], expr#4=[TRIM($t1, $t2, $t3)], EXPR$0=[$t4])
> EnumerableValues(tuples=[[{ 0 }]]) {code}
>
> Maybe we can just optimize it.
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