Attention: If you are using positional parameters with the query builder you have
to be very careful to bind all parameters in the order they appear in the SQL
statement , otherwise they get bound in the wrong order which can lead to serious
bugs in your code.
Example:
$qb = $conn->createQueryBuilder();
$qb->select('u.*')
->from('users', 'u')
->where('u.username = ' . $qb->createPositionalParameter('Foo', PDO::PARAM_STR))
->orWhere('u.username = ' . $qb->createPositionalParameter('Bar', PDO::PARAM_STR))