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https://issues.apache.org/jira/browse/CALCITE-7687?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18103161#comment-18103161
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Etienne Pelissier commented on CALCITE-7687:
--------------------------------------------
I plan to go back to working on this issue at the beginning of September.
> RelMdSelectivity and RelMdDistinctRowCount for Aggregate can propagate a
> predicate with wrong references
> --------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-7687
> URL: https://issues.apache.org/jira/browse/CALCITE-7687
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.42.0
> Reporter: Etienne Pelissier
> Assignee: Etienne Pelissier
> Priority: Minor
> Labels: in-progress, pull-request-available
>
> {{[RelMdSelectivity#getSelectivity|https://github.com/apache/calcite/blob/0211999427e294114db8f6b58cad95870cc13ccb/core/src/main/java/org/apache/calcite/rel/metadata/RelMdSelectivity.java#L178](Aggregate
> rel, RelMetadataQuery mq, @Nullable RexNode predicate)}} method:
> {code:java}
> public @Nullable Double getSelectivity(Aggregate rel, RelMetadataQuery mq,
> @Nullable RexNode predicate) {
> ...
> RelOptUtil.splitFilters(
> rel.getGroupSet(),
> predicate,
> pushable,
> notPushable);
> final RexBuilder rexBuilder = rel.getCluster().getRexBuilder();
> RexNode childPred =
> RexUtil.composeConjunction(rexBuilder, pushable, true);
> Double selectivity = mq.getSelectivity(rel.getInput(), childPred);
> ...
> }
> {code}
> {{[RelMdDistinctRowCount#getDistinctRowCount|https://github.com/apache/calcite/blob/0211999427e294114db8f6b58cad95870cc13ccb/core/src/main/java/org/apache/calcite/rel/metadata/RelMdDistinctRowCount.java#L168](Aggregate
> rel, RelMetadataQuery mq, ImmutableBitSet groupKey, @Nullable RexNode
> predicate)}} method:
> {code:java}
> public @Nullable Double getDistinctRowCount(Aggregate rel, RelMetadataQuery
> mq,
> ImmutableBitSet groupKey, @Nullable RexNode predicate) {
> ...
> RelOptUtil.splitFilters(
> ImmutableBitSet.range(rel.getGroupCount()),
> predicate,
> pushable,
> notPushable);
> final RexBuilder rexBuilder = rel.getCluster().getRexBuilder();
> RexNode childPreds =
> RexUtil.composeConjunction(rexBuilder, pushable, true);
> // set the bits as they correspond to the child input
> ImmutableBitSet.Builder childKey = ImmutableBitSet.builder();
> RelMdUtil.setAggChildKeys(groupKey, rel, childKey);
> Double distinctRowCount =
> mq.getDistinctRowCount(rel.getInput(), childKey.build(), childPreds);
> ...
> }
> {code}
> [CALCITE-4414|https://issues.apache.org/jira/browse/CALCITE-4414] fixed the
> analogous problem in RelMdSelectivity#getSelectivity for Calc: it pushes a
> predicate to its input, and RelOptUtil.pushPastCalc converts it to
> input-column references first, which is possible because Calc output fields
> are themselves expressions over the input.
> Aggregate's group-key output fields are also references to specific input
> fields, so predicates that reference only group keys can be translated the
> same way, via an analogous RelOptUtil.pushPastAggregate, which currently
> doesn't exist. Aggregate call outputs (e.g., COUNT(x\)) have no equivalent
> input expression, so a predicate referencing one must not be pushed at all.
> FilterAggregateTransposeRule already computes the same group-key mapping to
> push a Filter past an Aggregate, and can be used as a basis to implement the
> missing RelOptUtil.pushPastAggregate.
> The two examples below show the problem for
> RelMdSelectivity#getSelectivity(Aggregate) and
> RelMdDistinctRowCount#getDistinctRowCount(Aggregate), respectively.
> In both cases, the predicates reach the input with the wrong field
> references, silently returning statistics for the wrong column rather than
> raising an exception.
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