@Override
        public RelNode visit(FilterQueryOperation filter) {
            RexNode rexNode = convertExprToRexNode(filter.getCondition());
            return relBuilder.filter(rexNode).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