diff --git a/scripts/shift-old-datetimes-minus-8h.sql b/scripts/shift-old-datetimes-minus-8h.sql
index 193cb6d..40a59e1 100644
--- a/scripts/shift-old-datetimes-minus-8h.sql
+++ b/scripts/shift-old-datetimes-minus-8h.sql
@@ -1,26 +1,34 @@
--- Only devices.created_at / updated_at. first_seen_at / last_seen_at
--- were dropped (see 2026_08_04_000002_simplify_devices_columns).
---
--- 1) 备份 devices
--- 2) 把 @cutoff 改成切时区那一刻
--- 3) 先预览，再 START TRANSACTION … COMMIT
--- 4) 提交后：php artisan coruna:daily-stats --all
+-- Only devices.created_at / updated_at.
+-- 用 mysql -uroot -p -t -vv coruna < 本文件 才会打印行数。
+-- 已成功跑过就不要再跑（会再减 8 小时）。
+-- 改完后：php artisan coruna:daily-stats --all
 
 SET time_zone = '+08:00';
 SET @cutoff = '2026-09-16 14:00:00';  -- TODO: 改成实际切时区的时间
 
-SELECT 'created_at' AS col, COUNT(*) AS n, MIN(created_at) AS mn, MAX(created_at) AS mx
+SHOW COLUMNS FROM devices LIKE '%_at';
+
+SELECT 'preview' AS step, 'created_at' AS col, COUNT(*) AS n,
+       MIN(created_at) AS mn, MAX(created_at) AS mx
   FROM devices WHERE created_at IS NOT NULL AND created_at < @cutoff
-UNION ALL SELECT 'updated_at', COUNT(*), MIN(updated_at), MAX(updated_at)
+UNION ALL
+SELECT 'preview', 'updated_at', COUNT(*), MIN(updated_at), MAX(updated_at)
   FROM devices WHERE updated_at IS NOT NULL AND updated_at < @cutoff;
 
 START TRANSACTION;
 
 UPDATE devices SET created_at = DATE_SUB(created_at, INTERVAL 8 HOUR)
  WHERE created_at IS NOT NULL AND created_at < @cutoff;
+SELECT ROW_COUNT() AS created_at_updated;
+
 UPDATE devices SET updated_at = DATE_SUB(updated_at, INTERVAL 8 HOUR)
  WHERE updated_at IS NOT NULL AND updated_at < @cutoff;
+SELECT ROW_COUNT() AS updated_at_updated;
+
+SELECT id, device_id, created_at, updated_at
+  FROM devices
+ WHERE created_at IS NOT NULL
+ ORDER BY id ASC
+ LIMIT 3;
 
--- 后台看一台改时区前的设备，时间对了再 COMMIT
 COMMIT;
--- ROLLBACK;