I am getting "wide character in print" messages when I run this script. There is no wide character in the data

Maybe not in the data you get from the database, but surely in the data you print. You find it with something like

binmode STDOUT, ':encoding(UTF-8)';
print $str =~ /([^\0-\177]+)/g, "\n";
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There are lots of things that can turn ASCII-Data into non-ASCII data, including Encode::decode, JSON decoding and chr.