更新

backend/app/payroll/settings/router.py

@@ -204,6 +204,15 @@ def create_insurance_rate(rate: schemas.InsuranceRateCreate):
     """保険料率を作成"""
     with get_connection() as conn:
         with conn.cursor() as cur:
+            # 既存の同キー（rate_year, rate_type, calculation_target, prefecture）が存在しないか確認
+            cur.execute(
+                "SELECT 1 FROM insurance_rates WHERE rate_year = %s AND rate_type = %s AND calculation_target = %s AND prefecture = %s LIMIT 1",
+                (rate.rate_year, rate.rate_type, rate.calculation_target, rate.prefecture)
+            )
+            if cur.fetchone():
+                # 重複があればクライアントに分かりやすく 409 を返す
+                raise HTTPException(status_code=status.HTTP_409_CONFLICT, detail="指定された年度・種類・計算対象・都道府県の保険料率は既に存在します")
+
             cur.execute(
                 """
                 INSERT INTO insurance_rates (