"Column 'Value' in found." when fetching balance in query

Question

I’m building an ATM simulator, with the features of Deposit, Withdraw and Extract are functional. However, I’m not getting the balance.

I have the method emitirSaldo() which must receive the value calculated by the query. Follow the code:

public Extrato emitirSaldo(Extrato mod) {

    conex.conecta();
    conex.executeSQL

    ("SELECT (SELECT SUM(valor) FROM extrato where Transacao = 'Deposito') "
        + "- (SELECT SUM(valor) FROM extrato where Transacao = 'Saque')");

    try {

        conex.resultset.first();
        mod.setSaldo(conex.resultset.getString("Valor"));

        JOptionPane.showMessageDialog(null, "Saldo recebido.");

    } catch (SQLException ex) {

        JOptionPane.showMessageDialog(null, "Erro ao apresentar o saldo./nErro: " + ex);
    }

    conex.desconecta();

    return mod;

}

This method is called inside the preview button:

private void btnVisualizarActionPerformed(java.awt.event.ActionEvent evt) {                                              
    // TODO add your handling code here:


    model = control.emitirSaldo(model);

    lblSaldo.setText(model.getSaldo());


}

When I run the program, the error is shown:

"java.sql.Sqlexception: Column 'Value' no found."

However in the database there is the column Value:

How can I calculate the balance and present it in Formsaldo, by clicking on the View button?

Answer 1

I believe your query will not return a column called "value". Replace the row:

mod.setSaldo(conex.resultset.getString("Valor"));

for

mod.setSaldo(conex.resultset.getString(1)); 

because your query will return a column with the result and that column has no name. This "1" represents its index.