Explicitly state what happens if `order_by` is called more than once. (#8791)

* Explicitly state what happens if `order_by` is called more than once.

The existing docs cover how to clear existing `order_by` clauses but don't actually describe the behavior of calling `order_by` multiple times with different clauses.

* Also update Select.order_by.

1 files changed, 4 insertions, 3 deletions

diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index 488dfe721..23260a985 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -4096,9 +4096,10 @@ class GenerativeSelect(SelectBase, Generative):
 
             stmt = select(table).order_by(table.c.id, table.c.name)
 
-        All existing ORDER BY criteria may be cancelled by passing
-        ``None`` by itself.  New ORDER BY criteria may then be added by
-        invoking :meth:`_sql.Select.order_by` again, e.g.::
+        Calling this method multiple times is equivalent to calling it once
+        with all the clauses concatenated. All existing ORDER BY criteria may
+        be cancelled by passing ``None`` by itself.  New ORDER BY criteria may
+        then be added by invoking :meth:`_orm.Query.order_by` again, e.g.::
 
             # will erase all ORDER BY and ORDER BY new_col alone
             stmt = stmt.order_by(None).order_by(new_col)