support "SELECT *" for ORM queries

A :func:`_sql.select` construct that is passed a sole '*' argument for
``SELECT *``, either via string, :func:`_sql.text`, or
:func:`_sql.literal_column`, will be interpreted as a Core-level SQL
statement rather than as an ORM level statement. This is so that the ``*``,
when expanded to match any number of columns, will result in all columns
returned in the result. the ORM- level interpretation of
:func:`_sql.select` needs to know the names and types of all ORM columns up
front which can't be achieved when ``'*'`` is used.

If ``'*`` is used amongst other expressions simultaneously with an ORM
statement, an error is raised as this can't be interpreted correctly by the
ORM.

Fixes: #8235
Change-Id: Ic8e84491e14acdc8570704eadeaeaf6e16b1e870

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index eae06377f..9db90cb02 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -347,6 +347,7 @@ class ClauseElement(
     _is_lambda_element = False
     _is_singleton_constant = False
     _is_immutable = False
+    _is_star = False
 
     @property
     def _order_by_label_element(self) -> Optional[Label[Any]]:
@@ -2174,6 +2175,10 @@ class TextClause(
 
     _allow_label_resolve = False
 
+    @property
+    def _is_star(self):
+        return self.text == "*"
+
     def __init__(self, text: str):
         self._bindparams: Dict[str, BindParameter[Any]] = {}
 
@@ -4535,6 +4540,10 @@ class ColumnClause(
 
     _is_multiparam_column = False
 
+    @property
+    def _is_star(self):
+        return self.is_literal and self.name == "*"
+
     def __init__(
         self,
         text: str,