Create a new mysql user and grant them full priviledges to a specific database only.

mysql_user_grant.sql

-- This will be for ALL hosts, not just localhost, if you want it to only be for
--  localhost, then change 'codfish'@'%' to 'codfish'@'localhost'
CREATE USER 'codfish'@'%' IDENTIFIED BY 'password_here';
GRANT ALL PRIVILEGES ON `database_name`.* TO 'codfish'@'%';
FLUSH PRIVILEGES;