add_field_table example

$table_mapping = $this->getTableMapping();
      $field_definition = $this->getFieldStorageDefinition();

      foreach ($options as $column) {
        $fields[$column] = $table_mapping->getFieldColumnName($field_definition, $column);
      }

      $this->group_fields = $fields;
    }

    // Add additional fields (and the table join itself) if needed.     if ($this->add_field_table($use_groupby)) {
      $this->ensureMyTable();
      $this->addAdditionalFields($fields);
    }

    // Let the entity field renderer alter the query if needed.     $this->getEntityFieldRenderer()->query($this->query, $this->relationship);
  }

  /** * Determine if the field table should be added to the query. */