backporting a small bit of the changes made for the
2.0 version of #8796.

See if the changes apply cleanly to the 1.4 branch.

Fixes: #8796
Change-Id: I8118511a10beb38c545a55c962a18a77611293af

Fixed regression for 1.4 in :func:`_orm.contains_eager` where the "wrap in
subquery" logic of :func:`_orm.joinedload` would be inadvertently triggered
for use of the :func:`_orm.contains_eager` function with similar statements
(e.g. those that use ``distinct()``, ``limit()`` or ``offset()``). This is
not appropriate for :func:`_orm.contains_eager` which has always had the
contract that the user-defined SQL statement is unmodified with the
exception of adding the appropriate columns.

Also includes an adjustment to the assertion in Label._make_proxy()
which was there to prevent a fixed label name from being anonymized;
if the label is already anonymous, the change should proceed.
This logic was being hit before the contains_eager behavior was
adjusted. With the adjustment, this code is not used.

Fixes: #8569
Change-Id: I161e65041c0162fd2b83cbef40f57a50fcfaf0fd
(cherry picked from commit 57b400f07951f0ae8651ca38338ec5be1d222c7e)

Fixed bugs involving the :paramref:`.Table.include_columns` and the
:paramref:`.Table.resolve_fks` parameters on :class:`.Table`; these
little-used parameters were apparently not working for columns that refer
to foreign key constraints.

In the first case, not-included columns that refer to foreign keys would
still attempt to create a :class:`.ForeignKey` object, producing errors
when attempting to resolve the columns for the foreign key constraint
within reflection; foreign key constraints that refer to skipped columns
are now omitted from the table reflection process in the same way as
occurs for :class:`.Index` and :class:`.UniqueConstraint` objects with the
same conditions. No warning is produced however, as we likely want to
remove the include_columns warnings for all constraints in 2.0.

In the latter case, the production of table aliases or subqueries would
fail on an FK related table not found despite the presence of
``resolve_fks=False``; the logic has been repaired so that if a related
table is not found, the :class:`.ForeignKey` object is still proxied to the
aliased table or subquery (these :class:`.ForeignKey` objects are normally
used in the production of join conditions), but it is sent with a flag that
it's not resolvable. The aliased table / subquery will then work normally,
with the exception that it cannot be used to generate a join condition
automatically, as the foreign key information is missing. This was already
the behavior for such foreign key constraints produced using non-reflection
methods, such as joining :class:`.Table` objects from different
:class:`.MetaData` collections.

Fixes: #8100
Fixes: #8101

Change-Id: Ifa37a91bd1f1785fca85ef163eec031660d9ea4d
(cherry picked from commit 40e3c0da5be7dd526866bfc63590fc5621a9bd6e)

Added new attributes :attr:`.ValuesBase.returning_column_descriptions` and
:attr:`.ValuesBase.entity_description` to allow for inspection of ORM
attributes and entities that are installed as part of an :class:`.Insert`,
:class:`.Update`, or :class:`.Delete` construct. The
:attr:`.Select.column_descriptions` accessor is also now implemented for
Core-only selectables.

Fixes: #7861
Change-Id: Ia6a1cd24c798ba61f4e8e8eac90a0fd00d738342
(cherry picked from commit 2f1df5f9105149d6cb01c8b6ab6b9ccffa020780)

Adjusted the compiler's generation of "post compile" symbols including
those used for "expanding IN" as well as for the "schema translate map" to
not be based directly on plain bracketed strings with underscores, as this
conflicts directly with SQL Server's quoting format of also using brackets,
which produces false matches when the compiler replaces "post compile" and
"schema translate" symbols. The issue created easy to reproduce examples
both with the :meth:`.Inspector.get_schema_names` method when used in
conjunction with the
:paramref:`_engine.Connection.execution_options.schema_translate_map`
feature, as well in the unlikely case that a symbol overlapping with the
internal name "POSTCOMPILE" would be used with a feature like "expanding
in".

Fixes: #7300
Change-Id: I6255c850b140522a4aba95085216d0bca18ce230
(cherry picked from commit b919a0a85afd5066f9188b20ef06ee1b4af884a9)

Adjusted the "column disambiguation" logic that's new in 1.4, where the
same expression repeated gets an "extra anonymous" label, so that the logic
more aggressively deduplicates those labels when the repeated element
is the same Python expression object each time, as occurs in cases like
when using "singleton" values like :func:`_sql.null`.  This is based on
the observation that at least some databases (e.g. MySQL, but not SQLite)
will raise an error if the same label is repeated inside of a subquery.

Related to :ticket:`7153`, fixed an issue where result column lookups
would fail for "adapted" SELECT statements that selected for
"constant" value expressions most typically the NULL expression,
as would occur in such places as joined eager loading in conjunction
with limit/offset.  This was overall a regression due to issue
:ticket:`6259` which removed all "adaption" for constants like NULL,
"true", and "false", but this broke the case where the same adaption
logic were used to match the constant to a labeled expression referring
to the constant in a subquery.

Fixes: #7153
Fixes: #7154
Change-Id: I43823343721b9e70524ea3f5e8f39dd543a3e92b

Fixes: #7061
Change-Id: I715da89591c03d40d77734473bd42b34b9c4e1dc

Added new attribute :attr:`_sql.Select.columns_clause_froms` that will
retrieve the FROM list implied by the columns clause of the
:class:`_sql.Select` statement. This differs from the old
:attr:`_sql.Select.froms` collection in that it does not perform any ORM
compilation steps, which necessarily deannotate the FROM elements and do
things like compute joinedloads etc., which makes it not an appropriate
candidate for the :meth:`_sql.Select.select_from` method. Additionally adds
a new parameter
:paramref:`_sql.Select.with_only_columns.maintain_column_froms` that
transfers this collection to :meth:`_sql.Select.select_from` before
replacing the columns collection.

In addition, the :attr:`_sql.Select.froms` is renamed to
:meth:`_sql.Select.get_final_froms`, to stress that this collection is not
a simple accessor and is instead calculated given the full state of the
object, which can be an expensive call when used in an ORM context.

Additionally fixes a regression involving the
:func:`_orm.with_only_columns` function to support applying criteria to
column elements that were replaced with either
:meth:`_sql.Select.with_only_columns` or :meth:`_orm.Query.with_entities` ,
which had broken as part of :ticket:`6503` released in 1.4.19.

Fixes: #6808

Change-Id: Ib5d66cce488bbaca06dab4f68fb5cdaa73e8823e

Change-Id: I04057cc3d3f93de60b02999803e2ba6a23cdf68d