sub insert_entry {
    my $table=$_[0];    #table
    my $col=$_[1];
    my $entry=$_[2];    #value
    
    my $insert=sprintf(qq(INSERT INTO %s(%s) VALUES(%s) ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id)),
             $dbh->quote_identifier($table),
             $dbh->quote_identifier($col),
             $dbh->quote($entry));
    my $sth=$dbh->prepare($insert);
    $sth->execute();
    
    if ($sth->last_insert_id()){ #if new insertion
         return;
    }
    else {
         return $sth->last_insert_id(); #if duplicate return key
    }    
}