Reference to groups in a MySQL regex?

Question

How to reference to a group using a regex in MySQL? I tried:

REGEXP \'^(.)\\1$\'

but it does not work. How to do this?

Answer 1

You can't, there is no way to reference regex capturing groups in MySql.

Answer 2

(Old question, but top search result)

For MySQL 8:

SELECT REGEXP_REPLACE('stackoverflow','(.{5})(.*)','$2$1');
-- "overflowstack"

You can create capture groups with (), and you can refer to them using $1, $2, etc.