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https://issues.apache.org/jira/browse/CALCITE-6674?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17896713#comment-17896713
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Ruben Q L commented on CALCITE-6674:
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I have created a new PR with the approach suggested by [~julianhyde]:
https://github.com/apache/calcite/pull/4042
> Make RelDecorrelator rules configurable
> ---------------------------------------
>
> Key: CALCITE-6674
> URL: https://issues.apache.org/jira/browse/CALCITE-6674
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Ruben Q L
> Assignee: Ruben Q L
> Priority: Minor
> Labels: pull-request-available
> Fix For: 1.39.0
>
>
> RelDecorrelator decorrelates a query in two main steps:
> - First, a few Correlates cases are removed via rules (in
> {{removeCorrelationViaRule}} method).
> - Then, the main decorrelation logic is applied ({{{}decorrelateRel{}}}
> methods called by reflection).
> Currently, the rules applied on the first step are hardcoded, and cannot be
> configured.
> We are facing a situation where a Correlate is converted via one of these
> hardcoded rules (RemoveCorrelationForScalarAggregateRule), when in fact the
> main decorrelation logic (if the rule were not applied) would offer an
> arguably more beneficial plan:
> {noformat}
> -- Original (sub)plan
> LogicalCorrelate(correlation=[$cor0], joinType=[left], requiredColumns=[{0,
> 1}])
> LogicalJoin(condition=[=($0, $5)], joinType=[inner])
> LogicalTableScan(table=[[session, partsupp]])
> LogicalProject(p_partkey=[$0])
> LogicalFilter(condition=[LIKE($1, 'forest%':VARCHAR)])
> LogicalTableScan(table=[[session, part]])
> LogicalProject(EXPR$0=[*(0.50, $0)])
> LogicalAggregate(group=[{}], agg#0=[SUM($0)])
> LogicalProject(l_quantity=[$4])
> LogicalFilter(condition=[AND(=($1, $cor0.ps_partkey), =($2,
> $cor0.ps_suppkey), SEARCH($10, Sarg[[1994-01-01..1995-01-01)]))])
> LogicalTableScan(table=[[session, lineitem]])
> -- Decorrelation via RemoveCorrelationForScalarAggregateRule
> LogicalProject(ps_partkey=[$0], ps_suppkey=[$1], ps_availqty=[$2],
> ps_supplycost=[$3], ps_comment=[$4], p_partkey=[$5], $f6=[*(0.50, $6)])
> LogicalAggregate(group=[{0, 1, 2, 3, 4, 5}], agg#0=[SUM($6)])
> LogicalProject(ps_partkey=[$0], ps_suppkey=[$1], ps_availqty=[$2],
> ps_supplycost=[$3], ps_comment=[$4], p_partkey=[$5], l_quantity=[$10])
> LogicalJoin(condition=[AND(=($7, $0), =($8, $1), SEARCH($16,
> Sarg[[1994-01-01..1995-01-01)]))], joinType=[left])
> LogicalJoin(condition=[=($0, $5)], joinType=[inner])
> LogicalTableScan(table=[[session, partsupp]])
> LogicalProject(p_partkey=[$0])
> LogicalFilter(condition=[LIKE($1, 'forest%':VARCHAR)])
> LogicalTableScan(table=[[session, part]])
> LogicalProject(l_orderkey=[$0], l_partkey=[$1], l_suppkey=[$2],
> l_linenumber=[$3], l_quantity=[$4], l_extendedprice=[$5], l_discount=[$6],
> l_tax=[$7], l_returnflag=[$8], l_linestatus=[$9], l_shipdate=[$10],
> l_commitdate=[$11], l_receiptdate=[$12], l_shipinstruct=[$13],
> l_shipmode=[$14], l_comment=[$15], nullIndicator=[true])
> LogicalTableScan(table=[[session, lineitem]])
> -- -- Decorrelation via main logic (without
> RemoveCorrelationForScalarAggregateRule)
> LogicalJoin(condition=[AND(=($0, $6), =($1, $7))], joinType=[left])
> LogicalJoin(condition=[=($0, $5)], joinType=[inner])
> LogicalTableScan(table=[[session, partsupp]])
> LogicalProject(p_partkey=[$0])
> LogicalFilter(condition=[LIKE($1, 'forest%':VARCHAR)])
> LogicalTableScan(table=[[session, part]])
> LogicalAggregate(group=[{0, 1}], agg#0=[SUM($2)])
> LogicalProject(l_partkey=[$1], l_suppkey=[$2], l_quantity=[$4])
> LogicalFilter(condition=[AND(SEARCH($10,
> Sarg[[1994-01-01..1995-01-01)]), IS NOT NULL($1), IS NOT NULL($2))])
> LogicalTableScan(table=[[session, lineitem]])
> {noformat}
> The idea of this ticket is to make configurable the rules used by
> {{{}RelDecorrelator#removeCorrelationViaRule{}}}. By default, everything will
> behave as before (the same "default" rules will be applied), so we keep
> backwards compatibility; but we shall offer new methods to allow
> RelDecorrelator's caller to tune the rules to be used in this step.
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