diff --git a/migration.py b/migration.py
index df8d14c..e861199 100644
--- a/migration.py
+++ b/migration.py
@@ -35,6 +35,7 @@ def create_queries (
         table.integer ('model').comment ('GPT のモデル')
         table.datetime ('sent_at').comment ('送信日時')
         table.boolean ('answered').default (False).comment ('回答済')
+        table.foreign ('user_id').references ('user_id').on ('users').on_update ('cascade').on_delete ('restrict')
 
 
 def create_answers (
@@ -47,6 +48,7 @@ def create_answers (
         table.integer ('answer_type').comment ('回答区分')
         table.datetime ('sent_at').comment ('送信日時')
         table.boolean ('answered').default (False).comment ('回答済')
+        table.foreign ('query_id').references ('query_id').on ('queries').on_update ('cascade').on_delete ('restrict')
 
 
 def create_users (
@@ -57,6 +59,7 @@ def create_users (
         table.string ('code').comment ('ユーザ・コード（プラットフォーム依存）')
         table.string ('name').comment ('ユーザ名（プラットフォーム内）')
         table.binary ('icon').nullable ().comment ('アイコン')
+        table.unique (['platform', 'code'])
 
 
 def create_query_answer_histories (
@@ -65,6 +68,9 @@ def create_query_answer_histories (
         table.big_increments ('id')
         table.big_integer ('query_id')
         table.big_integer ('answer_id')
+        table.unique (['query_id', 'answer_id'])
+        table.foreign ('query_id').references ('query_id').on ('queries').on_update ('cascade').on_delete ('cascade')
+        table.foreign ('answer_id').references ('answer_id').on ('answers').on_update ('cascade').on_delete ('cascade')
 
 
 class DbConfig (TypedDict):