In your getCategories function, you can do some optimizations. fetchrow_hashref rather than fetchfow_array this will give you a hash by column so you don't have to. Use push which will get rid of the $row variable completely.

while (my $rh = $sth->fetchrow_hashref()) {
        push(@{$results_data}, $rh);
    }
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Unless there is a good reason to loop, you could replace loop in getCategories and just call selectall_hashref