I have a user, whom I want to grant all the READ permission on a db schema.
One way is this :
GRANT SELECT, SHOW_VIEW ON test.* TO \'readuser\'@\'%
Even user has got answer and @Michael - sqlbot has covered mostly points very well in his post but one point is missing, so just trying to cover it.
If you want to provide read permission to a simple user (Not admin kind of)-
GRANT SELECT, EXECUTE ON DB_NAME.* TO 'user'@'localhost' IDENTIFIED BY 'PASSWORD';
Note: EXECUTE is required here, so that user can read data if there is a stored procedure which produce a report (have few select statements).
Replace localhost with specific IP from which user will connect to DB.
Additional Read Permissions are-