SelectBase no longer a FromClause

As part of the SQLAlchemy 2.0 migration project, a conceptual change has
been made to the role of the :class:`.SelectBase` class hierarchy,
which is the root of all "SELECT" statement constructs, in that they no
longer serve directly as FROM clauses, that is, they no longer subclass
:class:`.FromClause`.  For end users, the change mostly means that any
placement of a :func:`.select` construct in the FROM clause of another
:func:`.select` requires first that it be wrapped in a subquery first,
which historically is through the use of the :meth:`.SelectBase.alias`
method, and is now also available through the use of
:meth:`.SelectBase.subquery`.    This was usually a requirement in any
case since several databases don't accept unnamed SELECT subqueries
in their FROM clause in any case.

See the documentation in this change for lots more detail.

Fixes: #4617
Change-Id: I0f6174ee24b9a1a4529168e52e855e12abd60667

1 files changed, 10 insertions, 4 deletions

diff --git a/lib/sqlalchemy/dialects/oracle/base.py b/lib/sqlalchemy/dialects/oracle/base.py
index 33f9c8659..842730c5b 100644
--- a/lib/sqlalchemy/dialects/oracle/base.py
+++ b/lib/sqlalchemy/dialects/oracle/base.py
@@ -886,7 +886,8 @@ class OracleCompiler(compiler.SQLCompiler):
                     [
                         c
                         for c in inner_subquery.c
-                        if orig_select.corresponding_column(c) is not None
+                        if orig_select.selected_columns.corresponding_column(c)
+                        is not None
                     ]
                 )
                 if (
@@ -939,17 +940,22 @@ class OracleCompiler(compiler.SQLCompiler):
                     limitselect._is_wrapper = True
 
                     if for_update is not None and for_update.of:
-
+                        limitselect_cols = limitselect.selected_columns
                         for elem in for_update.of:
-                            if limitselect.corresponding_column(elem) is None:
+                            if (
+                                limitselect_cols.corresponding_column(elem)
+                                is None
+                            ):
                                 limitselect = limitselect.column(elem)
 
                     limit_subquery = limitselect.alias()
+                    origselect_cols = orig_select.selected_columns
                     offsetselect = sql.select(
                         [
                             c
                             for c in limit_subquery.c
-                            if orig_select.corresponding_column(c) is not None
+                            if origselect_cols.corresponding_column(c)
+                            is not None
                         ]
                     )