Your code should work as it is.

The advice I can give you is the same you may find at Before asking a database related question ..., where it is outlined how to test your SQL before resorting to the script.

Additionally, you may see some different ways of creating an array from a DBI call in DBI Recipes.

My favorite is :

my $arrayref = $dbh->selectcol_arrayref($query);
[download]

HTH