form.h
Qt Code: 
  1. class form:public QDialog, Ui::form
  2. {
  3. 	Q_OBJECT
  4. 	public:
  5. 	bool isUpdate;
  6.        QString totaID;
  7.  	form(QWidget *parent = 0
  8.  			, const QString &uid = QString::nulll);
  9. 	public slots:
  10. 	double calculate(const QString &id);
  11. };
  12.  
  13. #endif
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form.cpp

Qt Code: 
  1. double form::calculate(const QString &id)
  2. {
  3. 	totaID = id;
  4. 	load();
  5.  
  6. 	return spin->value();
  7. }
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and after that I create a custom sqltablemodel

Qt Code: 
  1. QVariant CustomSql::data(const QModelIndex &index, int role) const
  2.       {
  3.       QVariant value = QSqlTableModel::data(index, role);
  4.       if (value.isValid() && role == Qt::DisplayRole) {
  5.       if (index.column() == 5){
  6.            calculate(index.sibling(index.row(),3).data().toString());
  7.            return QString("%L1").arg((d),0,'f',2).leftJustified(true);
  8.            }
  9.            return value.toString().leftJustified(true);
  10.       }
  11.       return value;
  12.  }
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am I clear?