USE database;

DROP TABLE IF EXISTS taxon;
CREATE TABLE taxon (t_id INT(n) PRIMARY KEY auto_increment,
                    [...]
                   );

DROP TABLE IF EXISTS node;
CREATE TABLE node (n_id INT(n) PRIMARY KEY auto_increment,
                   n_t_id INT(n) NOT NULL DEFAULT 0,
                   [...]
                  );

DROP TABLE IF EXISTS sequence;
CREATE TABLE sequence (s_id INT(n) PRIMARY KEY auto_increment,
                       s_t_id INTn) NOT NULL DEFAULT 0,
                       [...]
                      );

##</code><code>##

$dbh->selectall_arrayref("SELECT * FROM taxon, node WHERE n_t_id = t_id");

##</code><code>##

$dbh->selectrow_arrayref("SELECT * FROM node, taxon WHERE n_id = XXX AND t_id = n_t_id");