Why do I get undefined reference errors when trying to create a database?

I'm trying to create an SQLite database in Qt:

#include <QtCore/QCoreApplication>
#include <QtSql/QSqlDatabase>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
    db.setDatabaseName("C:\\Users\\Tanner\\Desktop\\db.sqlite");

    return a.exec();
}

The output:

C:\Users\Tanner\qt\sqltest-build-desktop..\sqltest\main.cpp:8: error: undefined reference to `_imp___ZN12QSqlDatabase17defaultConnectionE'

C:\Users\Tanner\qt\sqltest-build-desktop..\sqltest\main.cpp:8: error: undefined reference to `imp___ZN12QSqlDatabase11addDatabaseERK7QStringS2'

C:\Users\Tanner\qt\sqltest-build-desktop..\sqltest\main.cpp:8: error: undefined reference to `_imp___ZN12QSqlDatabaseD1Ev'

C:\Users\Tanner\qt\sqltest-build-desktop..\sqltest\main.cpp:9: error: undefined reference to `_imp___ZN12QSqlDatabase15setDatabaseNameERK7QString'

C:\Users\Tanner\qt\sqltest-build-desktop..\sqltest\main.cpp:11: error: undefined reference to `_imp___ZN12QSqlDatabaseD1Ev'

C:\Users\Tanner\qt\sqltest-build-desktop..\sqltest\main.cpp:11: error: undefined reference to `_imp___ZN12QSqlDatabaseD1Ev'

:-1: error: collect2: ld returned 1 exit status

I added extra slashes to the filepath because the compiler kept complaining about character escaping. Could that have anything to do with it? If so, how can I enter the path without it thinking I'm trying to escape the next character?

I was missing QT += sql in the .pro file.