title: In MYSQL, what does it mean when there are duplicate indices where everything but key_name is the same?
body: <pre><code>describe etc_category_metadata;
  
  +---------------------+---------------+------+-----+---------+----------------+
  | Field               | Type          | Null | Key | Default | Extra          |
  +---------------------+---------------+------+-----+---------+----------------+
  | id                  | int(11)       | NO   | PRI | NULL    | auto_increment |
  | user_id             | bigint(20)    | NO   |     | NULL    |                |
  | time_updated        | int(11)       | YES  |     | NULL    |                |
  | category_type       | int(11)       | YES  | MUL | NULL    |                |
  | status_keywords     | mediumblob    | YES  |     | NULL    |                |
  | page_keywords       | mediumblob    | YES  |     | NULL    |                |
  | profession_keywords | mediumblob    | YES  |     | NULL    |                |
  | adgroup_ids         | mediumblob    | YES  |     | NULL    |                |
  | prod                | tinyint(1)    | YES  |     | 0       |                |
  | version             | int(11)       | YES  |     | 1       |                |
  | status              | int(11)       | YES  |     | 0       |                |
  | dep_category_ids    | mediumblob    | YES  |     | NULL    |                |
  | custom_param        | mediumblob    | YES  |     | NULL    |                |
  | queue_priority      | int(11)       | YES  |     | 1       |                |
  | auto_requeue_num    | int(11)       | YES  |     | 0       |                |
  | cloned_version      | int(11)       | YES  |     | 0       |                |
  | custom_query        | varchar(1000) | YES  |     | NULL    |                |
  | description         | varchar(1000) | YES  |     | NULL    |                |
  | error_message       | mediumblob    | YES  |     | NULL    |                |
  | time_last_completed | int(11)       | YES  |     | NULL    |                |
  +---------------------+---------------+------+-----+---------+----------------+
  21 rows in set (0.40 sec)
  
  show index from etc_category_metadata;
  +-----------------------+------------+-----------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
  | Table                 | Non_unique | Key_name        | Seq_in_index | Column_name   | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
  +-----------------------+------------+-----------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
  | etc_category_metadata |          0 | PRIMARY         |            1 | id            | A         |       12613 |     NULL | NULL   |      | BTREE      |         |               |
  | etc_category_metadata |          0 | category_type   |            1 | category_type | A         |       12613 |     NULL | NULL   | YES  | BTREE      |         |               |
  | etc_category_metadata |          0 | category_type   |            2 | version       | A         |       12613 |     NULL | NULL   | YES  | BTREE      |         |               |
  | etc_category_metadata |          0 | category_type_2 |            1 | category_type | A         |       12613 |     NULL | NULL   | YES  | BTREE      |         |               |
  | etc_category_metadata |          0 | category_type_2 |            2 | version       | A         |       12613 |     NULL | NULL   | YES  | BTREE      |         |               |
  | etc_category_metadata |          0 | category_type_3 |            1 | category_type | A         |       12613 |     NULL | NULL   | YES  | BTREE      |         |               |
  | etc_category_metadata |          0 | category_type_3 |            2 | version       | A         |       12613 |     NULL | NULL   | YES  | BTREE      |         |               |
  +-----------------------+------------+-----------------+--------------+---------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
  7 rows in set (0.07 sec)
  </code></pre>
  
  <p>Trying to figure out whether it's safe to delete the keys <code>category_type_2</code> and <code>category_type_3</code>. It seems like they are the exact same indices as <code>category_type</code>. This is a legacy table that I have no idea who created a long time ago. Are there any valid reasons someone would end up creating these three keys that seem duplicates?</p>