From the DBI docs

$hash_ref = $dbh->selectall_hashref($statement, $key_field);

> > The $key_field parameter defines which column, or columns, are used as keys in the returned hash. It can either be the name of a single field, or a reference to an array containing multiple field names. Using multiple names yields a tree of nested hashes.

I think you either want to pass “Slice“ or [“Slice“]