Fixed #23753 -- Oracle failure with Coalesce

django/db/models/functions.py

@@ -16,6 +16,18 @@ class Coalesce(Func):
             raise ValueError('Coalesce must take at least two expressions')
         super(Coalesce, self).__init__(*expressions, **extra)
 
+    def as_oracle(self, compiler, connection):
+        # we can't mix TextField (NCLOB) and CharField (NVARCHAR), so convert
+        # all fields to NCLOB when we expect NCLOB
+        if self.output_field.get_internal_type() == 'TextField':
+            class ToNCLOB(Func):
+                function = 'TO_NCLOB'
+
+            expressions = [
+                ToNCLOB(expression) for expression in self.get_source_expressions()]
+            self.set_source_expressions(expressions)
+        return super(Coalesce, self).as_sql(compiler, connection)
+
 
 class ConcatPair(Func):
     """

tests/db_functions/tests.py

@@ -56,6 +56,18 @@ class FunctionTests(TestCase):
             lambda a: a.headline
         )
 
+        # mixed Text and Char wrapped
+        article = Article.objects.annotate(
+            headline=Coalesce(Lower('summary'), Lower('text'), output_field=TextField()),
+        )
+
+        self.assertQuerysetEqual(
+            article.order_by('title'), [
+                lorem_ipsum.lower(),
+            ],
+            lambda a: a.headline
+        )
+
     def test_concat(self):
         Author.objects.create(name='Jayden')
         Author.objects.create(name='John Smith', alias='smithj', goes_by='John')