support stringify for plain CTE

Altered the compilation for the :class:`.CTE` construct so that a string is
returned representing the inner SELECT statement if the :class:`.CTE` is
stringified directly, outside of the context of an enclosing SELECT; This
is the same behavior of :meth:`_FromClause.alias` and
:meth:`_SelectStatement.subquery`. Previously, a blank string would be
returned as the CTE is normally placed above a SELECT after that SELECT has
been generated, which is generally misleading when debugging.

Change-Id: Id3007c28e4a7a56d867e850bb890752946bd8f6f
References: #5988

1 files changed, 11 insertions, 0 deletions

diff --git a/test/sql/test_compiler.py b/test/sql/test_compiler.py
index 140de8622..acf16ca1c 100644
--- a/test/sql/test_compiler.py
+++ b/test/sql/test_compiler.py
@@ -4309,6 +4309,17 @@ class StringifySpecialTest(fixtures.TestBase):
             "SELECT anon_1.myid FROM anon_1",
         )
 
+    @testing.combinations(("cte",), ("alias",), ("subquery",))
+    def test_grouped_selectables_print_alone(self, modifier):
+        stmt = select(table1).where(table1.c.myid == 10)
+
+        grouped = getattr(stmt, modifier)()
+        eq_ignore_whitespace(
+            str(grouped),
+            "SELECT mytable.myid, mytable.name, "
+            "mytable.description FROM mytable WHERE mytable.myid = :myid_1",
+        )
+
     def test_next_sequence_value(self):
         # using descriptive text that is intentionally not compatible
         # with any particular backend, since all backends have different