Table schema

mysql> desc activation_code;
+----------------------------------+------------------+------+-----+-------------------+-----------------------------+
| Field                            | Type             | Null | Key | Default           | Extra                       |
+----------------------------------+------------------+------+-----+-------------------+-----------------------------+
| product_group_id                 | int(11)          | YES  | MUL | NULL              |                             |
| nid                              | int(10) unsigned | NO   | PRI | NULL              | auto_increment              |
| activation_code                  | varchar(255)     | YES  | MUL | NULL              |                             |
| uid                              | int(11)          | YES  | MUL | NULL              |                             |
| status                           | int(11)          | YES  |     | NULL              |                             |
| created                          | int(11)          | YES  |     | NULL              |                             |
| changed                          | int(11)          | YES  |     | NULL              |                             |
| field_activation_status_value    | varchar(20)      | YES  | MUL | NULL              |                             |
| field_code_activation_date_value | int(11)          | YES  |     | NULL              |                             |
| field_code_validity_period_value | int(11)          | YES  |     | NULL              |                             |
| field_expiration_date_value      | int(11)          | YES  |     | NULL              |                             |
| field_generation_date_value      | int(11)          | YES  |     | NULL              |                             |
| field_product_isbn_value         | varchar(100)     | YES  | MUL | NULL              |                             |
| field_user_name_uid              | int(10) unsigned | YES  | MUL | NULL              |                             |
+----------------------------------+------------------+------+-----+-------------------+-----------------------------+

mysql> desc field_data_field_isbn;
+-------------------+------------------+------+-----+---------+-------+
| Field             | Type             | Null | Key | Default | Extra |
+-------------------+------------------+------+-----+---------+-------+
| entity_type       | varchar(128)     | NO   | PRI |         |       |
| bundle            | varchar(128)     | NO   | MUL |         |       |
| deleted           | tinyint(4)       | NO   | PRI | 0       |       |
| entity_id         | int(10) unsigned | NO   | PRI | NULL    |       |
| revision_id       | int(10) unsigned | YES  | MUL | NULL    |       |
| language          | varchar(32)      | NO   | PRI |         |       |
| delta             | int(10) unsigned | NO   | PRI | NULL    |       |
| field_isbn_value  | varchar(255)     | YES  | MUL | NULL    |       |
| field_isbn_format | varchar(255)     | YES  | MUL | NULL    |       |
+-------------------+------------------+------+-----+---------+-------+