code: public function down(Schema $schema)
      {
          switch ($this->platform->getName()) {
              case 'postgresql':
                  $this->addSql('DROP SEQUENCE ds_config_id_seq CASCADE');
                  $this->addSql('DROP TABLE ds_config');
                  break;
  
              default:
                  $this->abortIf(true,'Migration cannot be executed on "'.$this->platform->getName().'".');
                  break;
          }
      }
docs: Down migration
  
  @param \Doctrine\DBAL\Schema\Schema $schema