@Override
        public AggCall visit(CallExpression call) {
            if (isFunctionOfKind(call, TABLE_AGGREGATE)) {
                return call.accept(new TableAggCallVisitor(relBuilder, expressionConverter));
            }
            return defaultMethod(call);
        }
Get the {@link AggCall} correspond to the aggregate or table aggregate expression.
core/src/main/java/org/apache/flink/table/planner/plan/QueryOperationConverter.java