joinAddExtra example

else {
      // This can be used if left_field is a formula or something. It should be used only *very* rarely.       $left_field = $this->leftField;
      $left_table = NULL;
    }

    $condition = "$left_field " . $this->configuration['operator'] . " $table[alias].$this->field";
    $arguments = [];

    // Tack on the extra.     if (isset($this->extra)) {
      $this->joinAddExtra($arguments, $condition, $table, $select_query, $left_table);
    }

    $select_query->addJoin($this->type, $right_table, $table['alias'], $condition, $arguments);
  }

  /** * Adds the extras to the join condition. * * @param array $arguments * Array of query arguments. * @param string $condition * The condition to be built. * @param array $table * The right table. * @param \Drupal\Core\Database\Query\SelectInterface $select_query * The current select query being built. * @param array $left_table * The left table. */