我无法使用javafx gui从数据库中删除记录

Question

我是Java的新手，我正在尝试使用javafx gui从我创建的数据库中删除记录。我已经将数据库中的数据显示在tableView上并执行了删除行，但它只删除了tableView中的行而没有删除数据库中的记录。

如何在按下删除按钮时从数据库中删除记录？

以下是删除按钮的代码：

@FXML
private void kDELac( ActionEvent event ) throws SQLException {
   allFiles = tableView.getItems();
   fileSelected = tableView.getSelectionModel().getSelectedItems();
   fileSelected.forEach( allFiles::remove );
   DatabaseHandler handler = DatabaseHandler.getInstance();
   handler.deleteRow(uniqueIdentifier);
}

...这里是负责从DB中删除的代码

private final String deleteQuery =
   "DELETE FROM BOOK WHERE <UNIQUE_COLUMN> = ?";

public void deleteRow( String uniqueIdentifier ) {
   Statement stmt = conn.createStatement();
   stmt.executeUpdate( deleteQuery + uniqueIdentifier + "'" );
   conn.commit();
}

负责从DB中删除的代码嵌入在DatabaseHandler.java类中：

public final class DatabaseHandler {

   private static DatabaseHandler handler=null;
   private static final String DB_URL = "jdbc:derby:database;create=true";
   private static Connection conn = null;
   private static Statement stmt = null;

   private DatabaseHandler() {
      createConnection();
      setupBookTable();
   }

   public static DatabaseHandler getInstance() {
      if( handler == null ) {
         handler = new DatabaseHandler();
      }
      return handler;
   }

   void createConnection() {
      class.forName("org.apache.derby.jdbc.EmbeddedDriver").newInstance();
      conn = DriverManager.getConnection(DB_URL);
   }

   void setupBookTable() {
      String TABLE_NAME = "BOOK";
      stmt = conn.createStatement();
      DatabaseMetaData dbm = conn.getMetaData();
      ResultSet tables =
         dbm.getTables( null, null, TABLE_NAME.toUpperCase(), null );
      if( tables.next()) {
         System.out.println("Table " + TABLE_NAME + "already exists." );
      }
      else {
         stmt.execute(
            "CREATE TABLE " + TABLE_NAME + "("
            + " id varchar(200) primary key,\n"
            + " title varchar(200),\n"
            + " author varchar(200),\n"
            + " publisher varchar(100),\n"
            + " isAvail boolean default true"
            + " )");
      }
   }

   public ResultSet execQuery(String query) {
      ResultSet result;
      stmt = conn.createStatement();
      result = stmt.executeQuery(query);
      return result;
   }

   public boolean execAction(String qu) {
      stmt = conn.createStatement();
      stmt.execute(qu);
      return true;
   }

   private final String deleteQuery =
      "DELETE FROM BOOK WHERE <UNIQUE_COLUMN> = ?";

   public void deleteRow(String uniqueIdentifier)  {
      Statement stmt = conn.createStatement(); 
      stmt.executeUpdate(deleteQuery + uniqueIdentifier + "'");
      conn.commit();
   }
}