public boolean isAggregationFunctionExpression() {
    return isBuiltInAggregationFunctionExpression() || isExternalAggregationFunctionExpression();
  }
Accessible for {@link ExpressionVisitor}, use {@link ExpressionVisitor#process} instead.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/Expression.java