MySQL Regular expression like wildcard _ regular expression

Some characters of the extended regular expression are:

“.” matches any single character.
A character class "[...]" Matches any character within the square brackets. For example, "[ABC]" matches "a", "B", or "C". To name a range of characters, use a "-". "[A-z]" matches any lowercase letter, and "[0-9]" matches any number.
"*" matches 0 or more things in front of it. For example, "x*" matches any number of "X" characters, "[0-9]*" matches any number of numbers, and ". *" matches any number of anything.
Regular expressions are case-sensitive, but if you want to, you can use a character class to match two ways of writing. For example, "[AA]" matches either lowercase or uppercase "a" and "[A-za-z]" matches any of the letters in both ways.
If it appears anywhere in the tested value, the pattern matches (as long as they match the entire value and the SQL pattern matches).
To locate a pattern so that it must match the start or end of the tested value, use "^" at the beginning of the pattern or at the end of the pattern with "$".
To illustrate how extended regular expressions work, the like query shown below uses RegExp overrides:
To find the name that begins with "B", use "^" to match the start of the first name and "[BB]" to match lowercase or uppercase "B":

Mysql> select * FROM pet WHERE name REGEXP "^[BB]";
+--------+--------+---------+------+------------+------------+
| name | Owner | Species | sex | Birth | Death |
+--------+--------+---------+------+------------+------------+
| Buffy | Harold | Dog | f | 1989-05-13 | NULL |
| Bowser | Diane | Dog | m | 1989-08-31 | 1995-07-29 |
+--------+--------+---------+------+------------+------------+
To find the name ending with "FY", use "$" to match the end of the name:
Mysql> select * FROM pet WHERE name REGEXP "fy$";
+--------+--------+---------+------+------------+-------+
| name | Owner | Species | sex | Birth | Death |
+--------+--------+---------+------+------------+-------+
| Fluffy | Harold | Cat | f | 1993-02-04 | NULL |
| Buffy | Harold | Dog | f | 1989-05-13 | NULL |
+--------+--------+---------+------+------------+-------+
To find the name containing a "W", use "[WW]" to match the lowercase or uppercase "W":
Mysql> SELECT * from pet WHERE name REGEXP "[WW]";
+----------+-------+---------+------+------------+------------+
| name | Owner | Species | sex | Birth | Death |
+----------+-------+---------+------+------------+------------+
| Claws | Gwen | Cat | m | 1994-03-17 | NULL |
| Bowser | Diane | Dog | m | 1989-08-31 | 1995-07-29 |
| Whistler | Gwen | Bird | NULL | 1997-12-09 | NULL |
+----------+-------+---------+------+------------+------------+
Since if a regular expression appears anywhere in the value and its pattern matches, there is no need to place a wildcard in the previous query on both sides of the pattern so that it matches the entire value, as if you were using an SQL schema.

To find names containing exactly 5 characters, use "^" and "$" to match the start and end of the first name, and the 5 "." Instances in between:
Mysql> select * FROM pet WHERE name REGEXP "^.....$";
+-------+--------+---------+------+------------+-------+
| name | Owner | Species | sex | Birth | Death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | Cat | m | 1994-03-17 | NULL |
| Buffy | Harold | Dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+
You can also rewrite the previous query by using the "{n}" "Repeat N-times" operator:
Mysql> SELECT * from pet WHERE name REGEXP "^. {5}$ ";
+-------+--------+---------+------+------------+-------+
| name | Owner | Species | sex | Birth | Death |
+-------+--------+---------+------+------------+-------+
| Claws | Gwen | Cat | m | 1994-03-17 | NULL |
| Buffy | Harold | Dog | f | 1989-05-13 | NULL |
+-------+--------+---------+------+------------+-------+