SET('value1','value2',...) [CHARACTER SET charset_name] [COLLATE
collation_name]

A set. A string object that can have zero or more values, each of which
must be chosen from the list of values 'value1', 'value2', ... SET
values are represented internally as integers.

A SET column can have a maximum of 64 distinct members. A table can
have no more than 255 unique element list definitions among its ENUM
and SET columns considered as a group. For more information on this
limit, see http://dev.mysql.com/doc/refman/5.7/en/limits-frm-file.html.

URL: http://dev.mysql.com/doc/refman/5.7/en/string-type-overview.html

