Select.php

1. 9.x drupal/core/lib/Drupal/Core/Database/Query/Select.php
2. 9.x drupal/core/lib/Drupal/Core/Database/Driver/mysql/Select.php
3. 9.x drupal/core/lib/Drupal/Core/Database/Driver/sqlite/Select.php
4. 9.x drupal/core/lib/Drupal/Core/Database/Driver/pgsql/Select.php

<?php

/**
 * @file
 * Definition of Drupal\Core\Database\Driver\sqlite\Select
 */
namespace Drupal\Core\Database\Driver\sqlite;

use Drupal\Core\Database\Query\Select as QuerySelect;
class Select extends QuerySelect {
  public function forUpdate($set = TRUE) {

    // SQLite does not support FOR UPDATE so nothing to do.
    return $this;
  }

}