JAVA Loop in loop and multi result sets closing first result set

Question

I have a problem with this code:

im = stat.executeQuery("SELECT * FROM imones");

        while (im.next()) {

            sask = stat2.executeQuery("SELECT * FROM saskaitos WHERE imone='" + im.getInt("id") + "'");
            while (sask.next()) {

                suma = suma + Integer.parseInt(sask.getString("suma"));

                kvit = stat3.executeQuery("SELECT * FROM kvitai WHERE sask_nr='" + sask.getInt("sask_nr") + "'");
                while (kvit.next()) {
                    suma = suma - Integer.parseInt(kvit.getString("suma"));
                }
                kvit.close();

            }
            sask.close();

            //if (suma > 0) {
            imone = im.getString("pav");
            skola = suma;
            DefaultTableModel y = (DefaultTableModel) pagrindinis.visos_skolos_table.getModel();
            Vector rowData = new Vector();

            rowData.add(imone);
            rowData.add(skola);
            y.addRow(rowData);
            //}
        }

        im.close();

I get only one loop ( while (im.next()) ) because 'sask' query has no results and it closes 'im' resultset and multi Statements not helping. How can I get this code working? Thank you!

Answer 1

The nested loops are not required, this can be done with one SQL statement that joins the table and sums the amounts. I obviously don't have all the column names at my disposal but you should be able to replace the names I've used with your own:

SELECT company.name,
       SUM(bill.amount) - SUM(cheque.amount) AS amount
FROM       imone     AS company
INNER JOIN saskaitos AS bill   ON company.id   = bill.imone
LEFT  JOIN kvitai    AS cheque ON bill.sask_nr = cheque.sask_nr
GROUP BY company.name;