#206 updated_at の並び順修正

backend/app/controllers/posts_controller.rb

@@ -65,15 +65,20 @@ class PostsController < ApplicationController
     end
 
     sort_sql =
-        if order[0] == 'original_created_at'
+        case order[0]
+        when 'original_created_at'
           'COALESCE(posts.original_created_before - INTERVAL 1 MINUTE,' +
           'posts.original_created_from,' +
-          'posts.created_at) ' +
-          order[1]
+          'posts.created_at) '
+        when 'updated_at'
+          'posts.updated_at_all'
         else
-          "posts.#{ order[0] } #{ order[1] }"
+          "posts.#{ order[0] }"
         end
-    posts = q.order(Arel.sql("#{ sort_sql }")).limit(limit).offset(offset).to_a
+    posts = q.order(Arel.sql("#{ sort_sql } #{ order[1] }, id #{ order[1] }"))
+             .limit(limit)
+             .offset(offset)
+             .to_a
 
     q = q.except(:select, :order)