Invoke column_expression() for subsequent SELECTs in CompoundSelect

Fixed bug where :meth:`.TypeEngine.column_expression` method would not be
applied to subsequent SELECT statements inside of a UNION or other
:class:`.CompoundSelect`, even though the SELECT statements are rendered at
the topmost level of the statement.   New logic now differentiates between
rendering the column expression, which is needed for all SELECTs in the
list, vs. gathering the returned data type for the result row, which is
needed only for the first SELECT.

Fixes: #4787
Change-Id: Iceb63e430e76d2365649aa25ead09c4e2a062e10

1 files changed, 30 insertions, 0 deletions

diff --git a/test/sql/test_type_expressions.py b/test/sql/test_type_expressions.py
index f913ab638..1f4649ffc 100644
--- a/test/sql/test_type_expressions.py
+++ b/test/sql/test_type_expressions.py
@@ -7,6 +7,7 @@ from sqlalchemy import String
 from sqlalchemy import Table
 from sqlalchemy import testing
 from sqlalchemy import TypeDecorator
+from sqlalchemy import union
 from sqlalchemy.testing import AssertsCompiledSQL
 from sqlalchemy.testing import eq_
 from sqlalchemy.testing import fixtures
@@ -272,6 +273,35 @@ class SelectTest(_ExprFixture, fixtures.TestBase, AssertsCompiledSQL):
             "test_table.y = outside_bind(inside_bind(:y_1))",
         )
 
+    def test_compound_select(self):
+        table = self._fixture()
+
+        s1 = select([table]).where(table.c.y == "hi")
+        s2 = select([table]).where(table.c.y == "there")
+
+        self.assert_compile(
+            union(s1, s2),
+            "SELECT test_table.x, lower(test_table.y) AS y "
+            "FROM test_table WHERE test_table.y = lower(:y_1) "
+            "UNION SELECT test_table.x, lower(test_table.y) AS y "
+            "FROM test_table WHERE test_table.y = lower(:y_2)",
+        )
+
+    def test_select_of_compound_select(self):
+        table = self._fixture()
+
+        s1 = select([table]).where(table.c.y == "hi")
+        s2 = select([table]).where(table.c.y == "there")
+
+        self.assert_compile(
+            union(s1, s2).alias().select(),
+            "SELECT anon_1.x, lower(anon_1.y) AS y FROM "
+            "(SELECT test_table.x AS x, test_table.y AS y "
+            "FROM test_table WHERE test_table.y = lower(:y_1) "
+            "UNION SELECT test_table.x AS x, test_table.y AS y "
+            "FROM test_table WHERE test_table.y = lower(:y_2)) AS anon_1",
+        )
+
 
 class DerivedTest(_ExprFixture, fixtures.TestBase, AssertsCompiledSQL):
     __dialect__ = "default"