I think you are looking for:

while (my $market = $market_sth->fetchrow_arrayref) {
    print "<option value=\"${market->[0]}\">${market->[0]}</option>" ;
}
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or something along those lines. You are returning into a scalar an should this be returning a scalar value from your db call. This will give you back a refernce to a single row of the return for each time through the while. Hence just reference the 0th element of the ar_ref and you'll have what you're looking for.