Qt+MySql. Why is exec not processed after prepare?

Question

MySQL

I'm trying to repeat the lesson with connecting to the database. Always used QSqlQuery::exec and it worked. In the example, before executing the query, pass the query string to QSqlQuery::prepare:

qry->prepare("SELECT position from pos;");
qry->exec();

when passing the received request to the model, I get empty lines.
If I do this: everything is displayed normally. Where to dig?
qry->exec("SELECT position from pos;");