Fix visit_label override to handle nested labels

pybigquery/sqlalchemy_bigquery.py

@@ -183,12 +183,19 @@ def visit_column(self, column, add_to_result_map=None,
                 self.preparer.quote(tablename) + \
                 "." + name
 
-    def visit_label(self, *args, **kwargs):
-        # Use labels in GROUP BY clause
-        if len(kwargs) == 0 or len(kwargs) == 1:
+    def visit_label(self, *args, within_group_by=False, **kwargs):
+        # Use labels in GROUP BY clause.
+        #
+        # Flag set in the group_by_clause method. Works around missing
+        # equivalent to supports_simple_order_by_label for group by.
+        if within_group_by:
             kwargs['render_label_as_label'] = args[0]
-        result = super(BigQueryCompiler, self).visit_label(*args, **kwargs)
-        return result
+        return super(BigQueryCompiler, self).visit_label(*args, **kwargs)
+
+    def group_by_clause(self, select, **kw):
+        return super(BigQueryCompiler, self).group_by_clause(
+            select, **kw, within_group_by=True
+        )
 
 
 class BigQueryTypeCompiler(GenericTypeCompiler):

test/test_sqlalchemy_bigquery.py

@@ -162,10 +162,14 @@ def query():
     def query(table):
         col1 = literal_column("TIMESTAMP_TRUNC(timestamp, DAY)").label("timestamp_label")
         col2 = func.sum(table.c.integer)
+        # Test rendering of nested labels. Full expression should render in SELECT, but
+        # ORDER/GROUP BY should use label only.
+        col3 = func.sum(func.sum(table.c.integer.label("inner")).label("outer")).over().label('outer')
         query = (
             select([
                 col1,
                 col2,
+                col3,
             ])
             .where(col1 < '2017-01-01 00:00:00')
             .group_by(col1)
@@ -297,6 +301,33 @@ def test_group_by(session, table, session_using_test_dataset, table_using_test_d
     assert len(result) > 0
 
 
+def test_nested_labels(engine, table):
+    col = table.c.integer
+    exprs = [
+        sqlalchemy.func.sum(
+            sqlalchemy.func.sum(col.label("inner")
+        ).label("outer")).over(),
+        sqlalchemy.func.sum(
+            sqlalchemy.case([[
+                sqlalchemy.literal(True),
+                col.label("inner"),
+            ]]).label("outer")
+        ),
+        sqlalchemy.func.sum(
+            sqlalchemy.func.sum(
+                sqlalchemy.case([[
+                    sqlalchemy.literal(True), col.label("inner")
+                ]]).label("middle")
+            ).label("outer")
+        ).over(),
+    ]
+    for expr in exprs:
+        sql = str(expr.compile(engine))
+        assert "inner" not in sql
+        assert "middle" not in sql
+        assert "outer" not in sql
+
+
 def test_session_query(session, table, session_using_test_dataset, table_using_test_dataset):
     for session, table in [(session, table), (session_using_test_dataset, table_using_test_dataset)]:
         col_concat = func.concat(table.c.string).label('concat')