A character between two other characters forms a range.
For example, [0-9] matches any decimal digit.
To include a literal ] character, it must immediately follow the opening bracket [.
To include a literal - character, it must be written first or last.
Any character that does not have a defined special meaning inside a [] pair matches only itself.
mysql>
mysql> SELECT 'aXbc' REGEXP '[a-dXYZ]';
+--------------------------+
| 'aXbc' REGEXP '[a-dXYZ]' |
+--------------------------+
| 1 |
+--------------------------+
1 row in set (0.00 sec)