Fixed #31271 -- Preserved ordering when unifying query parameters on Oracle.

This caused misplacing parameters in logged SQL queries.

Regression in 79065b55a7.

Thanks Hans Aarne Liblik for the report.

django/db/backends/oracle/base.py

@@ -500,7 +500,10 @@ class FormatStylePlaceholderCursor:
             # params_dict = {0.75: ':arg0', 2: ':arg1', 'sth': ':arg2'}
             # args = [':arg0', ':arg1', ':arg0', ':arg2', ':arg0']
             # params = {':arg0': 0.75, ':arg1': 2, ':arg2': 'sth'}
-            params_dict = {param: ':arg%d' % i for i, param in enumerate(set(params))}
+            params_dict = {
+                param: ':arg%d' % i
+                for i, param in enumerate(dict.fromkeys(params))
+            }
             args = [params_dict[param] for param in params]
             params = {value: key for key, value in params_dict.items()}
             query = query % tuple(args)

docs/releases/3.0.4.txt

@@ -20,3 +20,6 @@ Bugfixes
   related fields or parent link fields with :ref:`multi-table-inheritance` in
   the ``of`` argument, the corresponding models were not locked
   (:ticket:`31246`).
+
+* Fixed a regression in Django 3.0 that caused misplacing parameters in logged
+  SQL queries on Oracle (:ticket:`31271`).

tests/backends/tests.py

@@ -79,6 +79,10 @@ class LastExecutedQueryTest(TestCase):
         for qs in (
             Article.objects.filter(pk=1),
             Article.objects.filter(pk__in=(1, 2), reporter__pk=3),
+            Article.objects.filter(
+                pk=1,
+                reporter__pk=9,
+            ).exclude(reporter__pk__in=[2, 1]),
         ):
             sql, params = qs.query.sql_with_params()
             with qs.query.get_compiler(DEFAULT_DB_ALIAS).execute_sql(CURSOR) as cursor: