MySQL コマンドを使用して、show indexes from table_name一意のインデックスを見つけようとしています。しかし、すべてのインデックスが一意でないと誤って報告します。
mysql> desc books;
+------------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------------+--------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
| name | varchar(255) | YES | | NULL | |
| author_id | int(11) | YES | | NULL | |
| coauthor_id | int(11) | YES | | NULL | |
| publisher_id | int(11) | YES | | NULL | |
| isbn | varchar(255) | YES | | NULL | |
| publication_year | int(11) | YES | | NULL | |
| shelf_id | int(11) | YES | | NULL | |
+------------------+--------------+------+-----+---------+-------+
8 rows in set (0.00 sec)
mysql> show indexes from books;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| books | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)
mysql> create unique index books_isbn on books (isbn);
Query OK, 0 rows affected (0.23 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show indexes from books;
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| books | 0 | PRIMARY | 1 | id | A | 0 | NULL | NULL | | BTREE | | |
| books | 0 | books_isbn | 1 | isbn | A | 0 | NULL | NULL | YES | BTREE | | |
+-------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)
mysql> insert into books (id, name, isbn) values (0, 'foo', 'bar');
Query OK, 1 row affected, 1 warning (0.04 sec)
mysql> insert into books (id, name, isbn) values (1, 'foo2', 'bar');
ERROR 1062 (23000): Duplicate entry 'bar' for key 'books_isbn'
mysql>
show indexesが列に誤った情報を報告するのはなぜですか?non_uniqueまた、どのインデックスが一意であるかについて正しい答えを得るにはどうすればよいですか?
(これは MySQL 5.5.24 で、テーブルは InnoDB です。)