Fixed #18468 -- Added support for comments on columns and tables.

Thanks Jared Chung, Tom Carrick, David Smith, Nick Pope, and Mariusz
Felisiak for reviews.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Co-authored-by: Nick Pope <nick@nickpope.me.uk>

tests/introspection/tests.py

@@ -9,6 +9,7 @@ from .models import (
     City,
     Comment,
     Country,
+    DbCommentModel,
     District,
     Reporter,
     UniqueConstraintConditionModel,
@@ -179,6 +180,26 @@ class IntrospectionTests(TransactionTestCase):
             [connection.introspection.get_field_type(r[1], r) for r in desc],
         )
 
+    @skipUnlessDBFeature("supports_comments")
+    def test_db_comments(self):
+        with connection.cursor() as cursor:
+            desc = connection.introspection.get_table_description(
+                cursor, DbCommentModel._meta.db_table
+            )
+            table_list = connection.introspection.get_table_list(cursor)
+        self.assertEqual(
+            ["'Name' column comment"],
+            [field.comment for field in desc if field.name == "name"],
+        )
+        self.assertEqual(
+            ["Custom table comment"],
+            [
+                table.comment
+                for table in table_list
+                if table.name == "introspection_dbcommentmodel"
+            ],
+        )
+
     # Regression test for #9991 - 'real' types in postgres
     @skipUnlessDBFeature("has_real_datatype")
     def test_postgresql_real_type(self):