QSqlQuery Class Reference
[QtSql module]

Navigating records is performed with the following functions:

• next()
• previous()
• first()
• last()
• seek()

These functions allow the programmer to move forward, backward or arbitrarily through the records returned by the query. If you only need to move forward through the results (e.g., by using next()), you can use setForwardOnly(), which will save a significant amount of memory overhead and improve performance on some databases. Once an active query is positioned on a valid record, data can be retrieved using value(). All data is transferred from the SQL backend using QVariants.

For example:

     QSqlQuery query("SELECT country FROM artist");
     while (query.next()) {
         QString country = query.value(0).toString();
         doSomething(country);
     }

To access the data returned by a query, use value(int). Each field in the data returned by a SELECT statement is accessed by passing the field's position in the statement, starting from 0. This makes using SELECT * queries inadvisable because the order of the fields returned is indeterminate.

For the sake of efficiency, there are no functions to access a field by name (unless you use prepared queries with names, as explained below). To convert a field name into an index, use record().indexOf(), for example:

     QSqlQuery query("SELECT * FROM artist");
     int fieldNo = query.record().indexOf("country");
     while (query.next()) {
         QString country = query.value(fieldNo).toString();
         doSomething(country);
     }

QSqlQuery supports prepared query execution and the binding of parameter values to placeholders. Some databases don't support these features, so for those, Qt emulates the required functionality. For example, the Oracle and ODBC drivers have proper prepared query support, and Qt makes use of it; but for databases that don't have this support, Qt implements the feature itself, e.g. by replacing placeholders with actual values when a query is executed. Use numRowsAffected() to find out how many rows were affected by a non-SELECT query, and size() to find how many were retrieved by a SELECT.

Oracle databases identify placeholders by using a colon-name syntax, e.g :name. ODBC simply uses ? characters. Qt supports both syntaxes, with the restriction that you can't mix them in the same query.

You can retrieve the values of all the fields in a single variable (a map) using boundValues().

     QSqlQuery query;
     query.prepare("INSERT INTO person (id, forename, surname) "
                   "VALUES (:id, :forename, :surname)");
     query.bindValue(":id", 1001);
     query.bindValue(":forename", "Bart");
     query.bindValue(":surname", "Simpson");
     query.exec();

     QSqlQuery query;
     query.prepare("INSERT INTO person (id, forename, surname) "
                   "VALUES (:id, :forename, :surname)");
     query.bindValue(0, 1001);
     query.bindValue(1, "Bart");
     query.bindValue(2, "Simpson");
     query.exec();

     QSqlQuery query;
     query.prepare("INSERT INTO person (id, forename, surname) "
                   "VALUES (?, ?, ?)");
     query.bindValue(0, 1001);
     query.bindValue(1, "Bart");
     query.bindValue(2, "Simpson");
     query.exec();

     QSqlQuery query;
     query.prepare("INSERT INTO person (id, forename, surname) "
                   "VALUES (?, ?, ?)");
     query.addBindValue(1001);
     query.addBindValue("Bart");
     query.addBindValue("Simpson");
     query.exec();

     QSqlQuery query;
     query.prepare("CALL AsciiToInt(?, ?)");
     query.bindValue(0, "A");
     query.bindValue(1, 0, QSql::Out);
     query.exec();
     int i = query.boundValue(1).toInt(); // i is 65

 INSERT INTO testtable (id, name, samename) VALUES (:id, :name, :name)

     QMapIterator<QString, QVariant> i(query.boundValues());
     while (i.hasNext()) {
         i.next();
         cout << i.key().toAscii().data() << ": "
              << i.value().toString().toAscii().data() << endl;
     }

     QList<QVariant> list = query.boundValues().values();
     for (int i = 0; i < list.size(); ++i)
         cout << i << ": " << list.at(i).toString().toAscii().data() << endl;

     QSqlQuery query;
     query.exec("INSERT INTO employee (id, name, salary) "
                "VALUES (1001, 'Thad Beaumont', 65000)");

 QSqlQuery q;
 q.prepare("insert into myTable values (?, ?)");

 QVariantList ints;
 ints << 1 << 2 << 3 << 4;
 q.addBindValue(ints);

 QVariantList names;
 names << "Harald" << "Boris" << "Trond" << QVariant(QVariant::String);
 q.addBindValue(names);

 if (!q.execBatch())
     qDebug() << q.lastError();

 1  Harald
 2  Boris
 3  Trond
 4  NULL

     QSqlQuery query;
     query.prepare("INSERT INTO person (id, forename, surname) "
                   "VALUES (:id, :forename, :surname)");
     query.bindValue(":id", 1001);
     query.bindValue(":forename", "Bart");
     query.bindValue(":surname", "Simpson");
     query.exec();

 QSqlQuery q("select * from employees");
 QSqlRecord rec = q.record();

 qDebug() << "Number of columns: " << rec.count();

 int nameCol = rec.indexOf("name"); // index of the field "name"
 while (q.next())
     qDebug() << q.value(nameCol).toString(); // output all names

 SELECT forename, surname FROM people;