What data type should I use: ENUM, TINYINT, or CHAR?
ENUMs scare me because of any issue regarding adding/removing type values. You are probably better off representing both ProfessionalType and Decile as TINYINT or CHAR(3). Anything but ENUM.

See my past posts on ENUM :


Ocy 19, 2011 : Advantages and Disadvantages to using ENUM vs Integer types?
Jan 24, 2012 : Is it possible to change ENUM() lists?


For efficiency, please do not index this field alone, given such a low cardinality (8,10).