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https://issues.apache.org/jira/browse/FLINK-33996?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17804577#comment-17804577
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Benchao Li commented on FLINK-33996:
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bq. In addition, what I would like to ask is whether the current optimization
rule will definitely make the same project rewrite into the same cal node, at
least in my actual tests, this is the behavior.
[~hackergin] It's decided by the cost-based planner whether to merge it or not,
rules are only suggesting alternatives of the final results.
> Support disabling project rewrite when multiple exprs in the project
> reference the same sub project field.
> ----------------------------------------------------------------------------------------------------------
>
> Key: FLINK-33996
> URL: https://issues.apache.org/jira/browse/FLINK-33996
> Project: Flink
> Issue Type: Improvement
> Components: Table SQL / Runtime
> Affects Versions: 1.18.0
> Reporter: Feng Jin
> Priority: Major
> Labels: pull-request-available
>
> When multiple top projects reference the same bottom project, project rewrite
> rules may result in complex projects being calculated multiple times.
> Take the following SQL as an example:
> {code:sql}
> create table test_source(a varchar) with ('connector'='datagen');
> explain plan for select a || 'a' as a, a || 'b' as b FROM (select
> REGEXP_REPLACE(a, 'aaa', 'bbb') as a FROM test_source);
> {code}
> The final SQL plan is as follows:
> {code:sql}
> == Abstract Syntax Tree ==
> LogicalProject(a=[||($0, _UTF-16LE'a')], b=[||($0, _UTF-16LE'b')])
> +- LogicalProject(a=[REGEXP_REPLACE($0, _UTF-16LE'aaa', _UTF-16LE'bbb')])
> +- LogicalTableScan(table=[[default_catalog, default_database,
> test_source]])
> == Optimized Physical Plan ==
> Calc(select=[||(REGEXP_REPLACE(a, _UTF-16LE'aaa', _UTF-16LE'bbb'),
> _UTF-16LE'a') AS a, ||(REGEXP_REPLACE(a, _UTF-16LE'aaa', _UTF-16LE'bbb'),
> _UTF-16LE'b') AS b])
> +- TableSourceScan(table=[[default_catalog, default_database, test_source]],
> fields=[a])
> == Optimized Execution Plan ==
> Calc(select=[||(REGEXP_REPLACE(a, 'aaa', 'bbb'), 'a') AS a,
> ||(REGEXP_REPLACE(a, 'aaa', 'bbb'), 'b') AS b])
> +- TableSourceScan(table=[[default_catalog, default_database, test_source]],
> fields=[a])
> {code}
> It can be observed that after project write, regex_place is calculated twice.
> Generally speaking, regular expression matching is a time-consuming operation
> and we usually do not want it to be calculated multiple times. Therefore, for
> this scenario, we can support disabling project rewrite.
> After disabling some rules, the final plan we obtained is as follows:
> {code:sql}
> == Abstract Syntax Tree ==
> LogicalProject(a=[||($0, _UTF-16LE'a')], b=[||($0, _UTF-16LE'b')])
> +- LogicalProject(a=[REGEXP_REPLACE($0, _UTF-16LE'aaa', _UTF-16LE'bbb')])
> +- LogicalTableScan(table=[[default_catalog, default_database,
> test_source]])
> == Optimized Physical Plan ==
> Calc(select=[||(a, _UTF-16LE'a') AS a, ||(a, _UTF-16LE'b') AS b])
> +- Calc(select=[REGEXP_REPLACE(a, _UTF-16LE'aaa', _UTF-16LE'bbb') AS a])
> +- TableSourceScan(table=[[default_catalog, default_database,
> test_source]], fields=[a])
> == Optimized Execution Plan ==
> Calc(select=[||(a, 'a') AS a, ||(a, 'b') AS b])
> +- Calc(select=[REGEXP_REPLACE(a, 'aaa', 'bbb') AS a])
> +- TableSourceScan(table=[[default_catalog, default_database,
> test_source]], fields=[a])
> {code}
> After testing, we probably need to modify these few rules:
> org.apache.flink.table.planner.plan.rules.logical.FlinkProjectMergeRule
> org.apache.flink.table.planner.plan.rules.logical.FlinkCalcMergeRule
> org.apache.flink.table.planner.plan.rules.logical.FlinkProjectCalcMergeRule
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