Without this patch, Unicode columns get no special charset by default,
and fall back to whatever the table, database, server configuration
and (eventually) server hardcoded default encoding is.  The hardcoded
default mysql encoding is latin1.

This change maps Unicode to NVARCHAR (for consistency with other
sqlalchemy dialects), and UnicodeText to 'TEXT UNICODE'.

have been enhanced such that the function handler is now capable
of raising or returning a new exception object, which will replace
the exception normally being thrown by SQLAlchemy.
fixes #3076

fixes #3110

primary key change within a savepoint block would not
participate in being restored to their former state (not in
session, in session, previous PK) after the outer transaction
were rolled back. fixes #3108

as the attribute and probably just replaced itself, so that is
now _set_enable_single_crit
- as a side effect of the main issue fixed here, correct the case in
adjust_for_single_inheritance where the same mapper appears more
than once in mapper_adapter_map; run through a set() for uniqueness.
- Fixed bug in subquery eager loading in conjunction with
:func:`.with_polymorphic`, the targeting of entities and columns
in the subquery load has been made more accurate with respect
to this type of entity and others. Fixes #3106

the compiled cache is used.  That allows us to cache the whole metadata
and save on creating it at result time, when compiled cache is used.

system, whereby using a :class:`.TypeDecorator` in conjunction with
variant would fail with an MRO error when a comparison operator was used.
fixes #3102