@Override
        public RelNode visit(JoinQueryOperation join) {
            final Set<CorrelationId> corSet;
            if (join.isCorrelated()) {
                corSet = Collections.singleton(relBuilder.peek().getCluster().createCorrel());
            } else {
                corSet = Collections.emptySet();
            }

            return relBuilder.join(
                    convertJoinType(join.getJoinType()),
                    join.getCondition().accept(joinExpressionVisitor),
                    corSet)
                    .build();
        }
Get the {@link AggCall} correspond to the aggregate or table aggregate expression.
core/src/main/java/org/apache/flink/table/planner/plan/QueryOperationConverter.java