Refs #27090 -- Added real database sequence introspection.

Thanks Mariusz Felisiak for the Oracle part and Tim Graham for the
review.

tests/backends/postgresql/test_introspection.py

@@ -0,0 +1,23 @@
+import unittest
+
+from django.db import connection
+from django.test import TestCase
+
+from ..models import Person
+
+
+@unittest.skipUnless(connection.vendor == 'postgresql', "Test only for PostgreSQL")
+class DatabaseSequenceTests(TestCase):
+    def test_get_sequences(self):
+        cursor = connection.cursor()
+        seqs = connection.introspection.get_sequences(cursor, Person._meta.db_table)
+        self.assertEqual(
+            seqs,
+            [{'table': Person._meta.db_table, 'column': 'id', 'name': 'backends_person_id_seq'}]
+        )
+        cursor.execute('ALTER SEQUENCE backends_person_id_seq RENAME TO pers_seq')
+        seqs = connection.introspection.get_sequences(cursor, Person._meta.db_table)
+        self.assertEqual(
+            seqs,
+            [{'table': Person._meta.db_table, 'column': 'id', 'name': 'pers_seq'}]
+        )