rubenada commented on code in PR #4574:
URL: https://github.com/apache/calcite/pull/4574#discussion_r2421565203
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core/src/main/java/org/apache/calcite/rel/rules/SubQueryRemoveRule.java:
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@@ -895,12 +895,8 @@ private static void matchFilter(SubQueryRemoveRule rule,
LogicVisitor.find(RelOptUtil.Logic.TRUE, ImmutableList.of(c), e);
final Set<CorrelationId> variablesSet =
RelOptUtil.getVariablesUsed(e.rel);
- // Filter without variables could be handled before this change, we do
not want
- // to break it yet for compatibility reason.
- if (!filterVariablesSet.isEmpty()) {
- // Only consider the correlated variables which originated from this
sub-query level.
- variablesSet.retainAll(filterVariablesSet);
- }
+ // Only consider the correlated variables which originated from this
sub-query level.
Review Comment:
We can't do that because there's the possibility of a filter with
filter.getVariablesSet() = {$cor0, $cor1} whose condition is a combination of
two RexSubQueries: filter.getCondition = RexSubQuery0 (using $cor0) AND
RexSubQuery1 (using $cor1) ; thus when processing each RexSubQuery we need to
consider only the relevant variables ($cor0 for RexSubQuery0; and $cor1 for
RexSubQuery1).
Also, we can't simply use RexSubQuery's variables (via
RelOptUtil#getVariablesUsed) because it may happen that our RexSubQuery0 uses
$cor0 and $cor2, but this $cor2 belongs to the scope of a different filter (we
have nested correlated sub-queries); therefore we need the intersection between
the Filter's variableSet and the RexSubQuery's variableSet.
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