Selected rows data on tableview

I have created a Tableview in FXML file and populated the TableView. I have also create another FXML file StaffDetails that when I click on a row on the tableview the StaffDetails FXML fileLabels are inserted with that row's content. my problem is that for every row I click on the StaffDetails FXML file is insert with the content of row 1 only and not the content of the row I click on.. Please below is the code.

viewEmployee.setOnMouseClicked(e->{

    try {
        Employee user =(Employee)viewEmployee.getSelectionModel().getSelectedItem();
        String details="select *from Employee where STAFFID =?";
        pstmt=conn.prepareStatement(details);
        pstmt.setString(1,user.getStaffId());
        rs=pstmt.executeQuery();


        Stage stage = new Stage();
        Parent root = FXMLLoader.load(getClass().getResource("StaffDetails.fxml"));

        Scene scene = new Scene(root);

        stage.setScene(scene);

        stage.show();

@Override
public void initialize(URL location, ResourceBundle resources) {

    try {
        Class.forName("org.apache.derby.jdbc.ClientDriver");
        conn=DriverManager.getConnection("jdbc:derby://localhost:1527/Employee","Conduct","ccb");

        String details="select *from Employee";
        pstmt=conn.prepareStatement(details);

        rs=pstmt.executeQuery();

        rs.next();

        st.setText(rs.getString("staffId"));
        su.setText(rs.getString("surname"));
        fn.setText(rs.getString("firstName"));
        on.setText(rs.getString("otherNames"));
        db.setText(rs.getString("dateOfBirth"));
        sx.setText(rs.getString("sex"));