silundong commented on code in PR #4691:
URL: https://github.com/apache/calcite/pull/4691#discussion_r2629267265
##########
core/src/main/java/org/apache/calcite/sql2rel/RelFieldTrimmer.java:
##########
@@ -634,7 +634,23 @@ public TrimResult trimFields(
RelOptUtil.InputFinder inputFinder =
new RelOptUtil.InputFinder(inputExtraFields, fieldsUsed);
conditionExpr.accept(inputFinder);
- final ImmutableBitSet inputFieldsUsed = inputFinder.build();
+
+ // Collect all the SubQueries in the filter condition.
+ List<RexSubQuery> subQueries = RexUtil.SubQueryCollector.collect(filter);
+ // Get all the correlationIds present in the SubQueries
+ Set<CorrelationId> correlationIds =
RelOptUtil.getVariablesUsed(subQueries);
+ ImmutableBitSet requiredColumns = ImmutableBitSet.of();
+ if (!correlationIds.isEmpty()) {
+ // Correlation columns are also needed by SubQueries, so add them to
inputFieldsUsed.
+ requiredColumns =
RelOptUtil.correlationColumns(correlationIds.iterator().next(), filter);
Review Comment:
I'm not sure if this works correctly when nested correlations.
`RelOptUtil.getVariablesUsed` will return all CorrelationIds except those
generated within the subquery, so `correlationIds` may be have multiple
elements. For example:
```
select deptno, right_q.ename from emp e1, LATERAL (
select ename from emp e2 where exists(
select * from emp e3 where e1.sal = e3.sal and e2.empno = e3.empno))
right_q
LogicalProject(DEPTNO=[$7], ENAME=[$8])
LogicalCorrelate(correlation=[$cor0], joinType=[inner],
requiredColumns=[{5}])
LogicalTableScan(table=[[scott, EMP]])
LogicalProject(ENAME=[$1])
LogicalFilter(condition=[EXISTS({ <--------
LogicalFilter(condition=[AND(=($cor0.SAL, $5), =($cor1.EMPNO, $0))])
LogicalTableScan(table=[[scott, EMP]])
})], variablesSet=[[$cor1]])
LogicalTableScan(table=[[scott, EMP]])
```
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