mysql> EXPLAIN SELECT `doc_pk`, `doc_titulo_es`, `doc_fecha_alta`, `m_museo`.`m_
nombre_es`, `cdoc_cat_docum`.`cdoc_nombre_es` FROM `doc_documento`, `m_museo`, `
cdoc_cat_docum` WHERE `doc_documento`.`m_pk` = `m_museo`.`m_pk` AND `doc_documen
to`.`cdoc_pk` = `cdoc_cat_docum`.`cdoc_pk`  ORDER by doc_pk DESC LIMIT 0,10;
+----+-------------+----------------+--------+---------------+---------+--------
-+-----------------------------+------+---------------------------------+
| id | select_type | table          | type   | possible_keys | key     | key_len
 | ref                         | rows | Extra                           |
+----+-------------+----------------+--------+---------------+---------+--------
-+-----------------------------+------+---------------------------------+
|  1 | SIMPLE      | cdoc_cat_docum | ALL    | PRIMARY       | NULL    | NULL
 | NULL                        |    5 | Using temporary; Using filesort |
|  1 | SIMPLE      | doc_documento  | ref    | m_pk,cdoc_pk  | cdoc_pk | 4
 | oamc.cdoc_cat_docum.cdoc_pk |   42 |                                 |
|  1 | SIMPLE      | m_museo        | eq_ref | PRIMARY       | PRIMARY | 4
 | oamc.doc_documento.m_pk     |    1 |                                 |
+----+-------------+----------------+--------+---------------+---------+--------
-+-----------------------------+------+---------------------------------+
3 rows in set (0.02 sec)