my $sql = "select confidence_str from $table where probeset_id = ?";
if (!$dbh->prepare($sql)) {
   warn "error parsing SQL: $sql\n". $dbh->errstr;
   return;
}
if (!$dbh->execute($param)) {
   warn "error executing SQL: $sql\nparam $param\n". $dbh->errstr;
   return;
}