Adding the new MySQL user

Connect to your database as root, then add your new user like so:

CREATE USER 'tester'@'%' IDENTIFIED BY 'password';

The % here means the user 'tester' connecting from any host, you can place a network hostname here instead if you want to restrict access further. Naturally you will also want to substitute password with something a little stronger ;-)

Now run the following to grant the SELECT privilage to the new user on all databases:

GRANT SELECT ON *.* TO 'tester'@'%';

Or if you want to restrict access to only one database:

GRANT SELECT ON DATABASE.* TO 'tester'@'%';

Confirming that it worked

Connect as the new user:

mysql -u tester -p

And now see if you can update a record:

mysql> USE alpha;
mysql> UPDATE Person SET version_num = 5 WHERE OID = 1;
ERROR 1142 (42000): UPDATE command denied TO USER 'tester'@'localhost' FOR TABLE 'Person'

http://www.alphadevx.com/a/388-Adding-a-read-only-MySQL-user