improve targeting and labeling for unary() in columns clause

Fixed regression where usage of the standalone :func:`_sql.distinct()` used
in the form of being directly SELECTed would fail to be locatable in the
result set by column identity, which is how the ORM locates columns. While
standalone :func:`_sql.distinct()` is not oriented towards being directly
SELECTed (use :meth:`_sql.select.distinct` for a regular
``SELECT DISTINCT..``) , it was usable to a limited extent in this way
previously (but wouldn't work in subqueries, for example). The column
targeting for unary expressions such as "DISTINCT <col>" has been improved
so that this case works again, and an additional improvement has been made
so that usage of this form in a subquery at least generates valid SQL which
was not the case previously.

The change additionally enhances the ability to target elements in
``row._mapping`` based on SQL expression objects in ORM-enabled
SELECT statements, including whether the statement was invoked by
``connection.execute()`` or ``session.execute()``.

Fixes: #6008
Change-Id: I5cfa39435f5418861d70a7db8f52ab4ced6a792e

1 files changed, 3 insertions, 1 deletions

diff --git a/lib/sqlalchemy/engine/cursor.py b/lib/sqlalchemy/engine/cursor.py
index a9933c7ae..b5b92b171 100644
--- a/lib/sqlalchemy/engine/cursor.py
+++ b/lib/sqlalchemy/engine/cursor.py
@@ -1290,7 +1290,9 @@ class BaseCursorResult(object):
                 compiled
                 and compiled._result_columns
                 and context.cache_hit is context.dialect.CACHE_HIT
-                and not compiled._rewrites_selected_columns
+                and not context.execution_options.get(
+                    "_result_disable_adapt_to_context", False
+                )
                 and compiled.statement is not context.invoked_statement
             ):
                 metadata = metadata._adapt_to_context(context)