Given a cast ID, this method will return the associated
type (INT(10) or VARCHAR for instance). The returned type
can be processed by the Query Writer to build the specified
column for you in the database. The Cast ID is actually just
a superset of the QueryWriter types. In addition to default
Query Writer column types you can pass the following 'cast types':
'id' and 'string'. These will map to Query Writer specific
column types (probably INT and VARCHAR).