As ropey mentioned, remove the password in your post.

Also, the RaiseError attribute should be set in the connect statement (not after the ||):

my $dbh = DBI->connect(
    'DBI:mysql:nikos_db',
    'username',
    'password',
    {RaiseError=>1}
) || die $DBI::err;
[download]

Then if the connect fails, it will die with the error reported from the $DBI::err variable.