MySQL connects but doesn't queries, it queries if I do...

[Raccoon29]

Hi all,

I never saw this behavior before, so I'm a well bit confused, maybe I'm missing something stupid.
I built a minimal application just to test QMYSQL driver to use it in another project; the problem is that it connects, but queries are executed or not depending on how I do it:

-QSqlQuery::exec(QString query); -> works
-QSqlQuery::prepare(QString query); QSqlQuery::exec(); -> doesn't

no errors from the db, it just fails.
Someone knows why whould happen something like that?

This is the code I use:

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setHostName("localhost");
db.setDatabaseName("dbname");
db.setUserName("username");
db.setPassword("password");
bool ok = db.open();
if(ok)
{
    QMessageBox::information(this,"Connected","Database is connected");
    QSqlQuery query(db);
    query.prepare("SELECT * FROM categories");
    if(!query.exec()) // instruction: query.exec("SELECT * FROM categories") would work
          QMessageBox::critical(this,"Query error",db.lastError().text()); //no errors... but fails
    db.close();
}
else
    QMessageBox::critical(this,"Connect error",db.lastError().text());

QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
db.setHostName("localhost");
db.setDatabaseName("dbname");
db.setUserName("username");
db.setPassword("password");
bool ok = db.open();
if(ok)
{
    QMessageBox::information(this,"Connected","Database is connected");
    QSqlQuery query(db);
    query.prepare("SELECT * FROM categories");
    if(!query.exec()) // instruction: query.exec("SELECT * FROM categories") would work
          QMessageBox::critical(this,"Query error",db.lastError().text()); //no errors... but fails
    db.close();
}
else
    QMessageBox::critical(this,"Connect error",db.lastError().text());

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By the way, categories table exists in that db.

Anybody? Thanks in advance