code: public function getLast(): array
      {
          $sql = "select migration from {$this->table} as b
                  where exists (select max(batch) from {$this->table} as a where b.batch = a.batch) 
                  order by migration desc";
  
          $stmt = $this->pdo->prepare($sql);
          $stmt->execute();
  
          return $stmt->fetchAll(PDO::FETCH_COLUMN);
      }
docs: Get the last migration batch.
  
  @return array