behavior as that of :class:`.mysql.ENUM`.  Quotes are not required when
setting up the value, but quotes that are present will be auto-detected
along with a warning.  This also helps with Alembic where
the SET type doesn't render with quotes. [ticket:2817]

if it was generated from a :class:`.Column` that didn't specify ``unique``
(where it defaults to ``None``).  The flag will now always be ``True`` or
``False``. [ticket:2825]

Perform fewer dict lookups - tiny microoptimization

This enables the subquery eager loader strategy to apply a DISTINCT
to the innermost SELECT subquery, to assist in the case where
duplicate rows are generated by the innermost query which corresponds
to this relationship (there's not yet a general solution to the issue
of dupe rows within subquery eager loading, however, when joins outside
of the innermost subquery produce dupes).  When the flag
is set to ``True``, the DISTINCT is rendered unconditionally, and when
it is set to ``None``, DISTINCT is rendered if the innermost relationship
targets columns that do not comprise a full primary key.
The option defaults to False in 0.8 (e.g. off by default in all cases),
None in 0.9 (e.g. automatic by default).   Thanks to Alexander Koval
for help with this. [ticket:2836]

query string to override those defaults set up in the connect,
including "buffered" and "raise_on_warnings".
[ticket:2515]

rendered in the column list of a CREATE INDEX statement.
[ticket:2742]