I would like to copy the meta_value from row to another (in the same table) where the user_id matches.

Each user in the wp_usermeta table has a meta_key/meta_value pair for first_name and a meta_key/meta_value pair for shipping_first_name. I would like to copy the shipping_first_name value to the first_name value where the user_id matches.

How should this MySQL query be written?