Qt Databases (MySQL)

connection.cpp

//Create a default connection
QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");    //Or whatever database in use

/*We could add a second argument which is the connection name**
Example:
QSqlDatabase firstDB = QSqlDatabase::addDatabase("QMYSQL", "first");
*/

//Set connection information
db.setHostName("xxx.xxx.xxx.xxx");    //localhost if it's local
db.setDatabaseName("flightdb");
db.setUserName("acarlson");
db.setPassword("1uTbSbAs");

//Open it for use
if ( !db.open() )
QString error = db.lastError().text(); //Returns databaseText() and driverText() concatenated into a single string

/*Once a connection is established, we can call the static function QSqlDatabase::database()
from anywhere with a connection name to get a pointer to that database connection.
If we don't pass a connection name, it will return the default connection.*/

QSqlDatabase defaultDB = QSqlDatabase::database();

//OR
//QSqlDatabase firstDB = QSqlDatabase::database("first");


//Closing the connection
db.close();         //Close the database
db.removeDatabase() //Remove it

query.cpp

/****http://doc.qt.digia.com/4.7/sql-sqlstatements.html****/

//The QSqlQuery constructor accepts an optional QSqlDatabase object that specifies which database connection to use.
//If we don't specify any connection, so the default connection is used.

QSqlQuery query;
query.exec("SELECT name, salary FROM employee WHERE salary > 50000");
//If an error occurs, exec() returns false. The error is then available as QSqlQuery::lastError().


//Navigate through the result set

// QSqlQuery's internal pointer is located one position before the first record.
//We must call QSqlQuery::next() once to advance to the first record
//then next() again repeatedly to access the other records, until it returns false.

while (query.next())
{
    //QVariant QSqlQuery::value ( int index ) Returns the value of field index in the current record
    QString name = query.value(0).toString();   //1st result column (index 1)
    int salary = query.value(1).toInt();        //2d result column (index 2)
}

/*-----------------------------------------------------------------------*/
//How many results do we have
QSqlQuery query;
int numRows;
query.exec("SELECT name, salary FROM employee WHERE salary > 50000");

QSqlDatabase defaultDB = QSqlDatabase::database();

if (defaultDB.driver()->hasFeature(QSqlDriver::QuerySize)) {
   numRows = query.size();
}
else
{
   // this can be very slow
   query.last();
   numRows = query.at() + 1;
}

sql.pro

QT += core gui
QT += sql

Create MySQL driver for Qt on Windows
http://www.seppemagiels.com/blog/create-mysql-driver-qt-windows