之前一直有過疑惑為什麼MySQL資料庫存timestamp可以無視時區問題.
在業務中也是一直使用Laravel框架,內建的Migration也是使用的timestamp型別欄位,也沒太關心.

開始

檢視當前資料庫時區

mysql> show variables like "%time_zone%";
+------------------+--------+
| Variable_name  | Value |
+------------------+--------+
| system_time_zone | CST  |
| time_zone    | +08:00 |
+------------------+--------+
2 rows in set (0.30 sec)

查看錶結構

mysql> desc timestamp_test;
+--------------+-----------+------+-----+---------+----------------+
| Field    | Type   | Null | Key | Default | Extra     |
+--------------+-----------+------+-----+---------+----------------+
| id      | int    | NO  | PRI | NULL  | auto_increment |
| created_time | datetime | YES |   | NULL  |        |
| created_at  | timestamp | YES |   | NULL  |        |
+--------------+-----------+------+-----+---------+----------------+
3 rows in set (0.26 sec)

插入資料

mysql> insert into timestamp_test(created_time,created_at) values('2020-12-09 08:00:00','2020-12-09 08:00:00');
Query OK,1 row affected (0.22 sec)


mysql> select * from timestamp_test;
+----+---------------------+---------------------+
| id | created_time    | created_at     |
+----+---------------------+---------------------+
| 1 | 2020-12-09 08:00:00 | 2020-12-09 08:00:00 |
+----+---------------------+---------------------+
1 row in set (0.06 sec)

這個時間看起來是沒問題的,那麼我們嘗試修改時區再插入資料

mysql> SET time_zone = "+00:00";
Query OK,0 rows affected (0.03 sec)

mysql> insert into timestamp_test(created_time,1 row affected (0.03 sec)

mysql> SET time_zone = "+08:00";
Query OK,0 rows affected (0.04 sec)

這時候再檢視資料,兩條插入的SQL是一樣的,但是發現查詢的結果是不一樣的
這兩條資料created_at的相差正好是時區的時間差

mysql> select * from timestamp_test;
+----+---------------------+---------------------+
| id | created_time    | created_at     |
+----+---------------------+---------------------+
| 1 | 2020-12-09 08:00:00 | 2020-12-09 08:00:00 |
| 2 | 2020-12-09 08:00:00 | 2020-12-09 16:00:00 |
+----+---------------------+---------------------+
2 rows in set (0.06 sec)

再看一下實際儲存的時間戳,然後我們變化時區,發現欄位時間變化了,但是原始的時間戳資料沒變

mysql> select *,unix_timestamp(created_at) from timestamp_test;
+----+---------------------+---------------------+----------------------------+
| id | created_time    | created_at     | unix_timestamp(created_at) |
+----+---------------------+---------------------+----------------------------+
| 1 | 2020-12-09 08:00:00 | 2020-12-09 08:00:00 |         1607472000 |
| 2 | 2020-12-09 08:00:00 | 2020-12-09 16:00:00 |         1607500800 |
+----+---------------------+---------------------+----------------------------+
2 rows in set (0.06 sec)

mysql> SET time_zone = "+00:00";
Query OK,0 rows affected (0.09 sec)

mysql> show variables like "%time_zone%";
+------------------+--------+
| Variable_name  | Value |
+------------------+--------+
| system_time_zone | CST  |
| time_zone    | +00:00 |
+------------------+--------+
2 rows in set (0.08 sec)

mysql> select *,unix_timestamp(created_at) from timestamp_test;
+----+---------------------+---------------------+----------------------------+
| id | created_time    | created_at     | unix_timestamp(created_at) |
+----+---------------------+---------------------+----------------------------+
| 1 | 2020-12-09 08:00:00 | 2020-12-09 00:00:00 |         1607472000 |
| 2 | 2020-12-09 08:00:00 | 2020-12-09 08:00:00 |         1607500800 |
+----+---------------------+---------------------+----------------------------+
2 rows in set (0.18 sec)

因為這一切是MySQL隱式的幫我們轉換了,讓我們不用關心時區的問題

就是資料庫實際上會儲存 UTC 時間戳，寫入的時候先按 Session 時區轉成 UTC 時間，讀出的時候再按 Session 時區轉成當前時區的時間，這些轉換都是透明的

• 假如我們在正八區儲存了2020-12-09 08:00:00時間的一條資料
• 我們在正八區取出這一條資料,時間依然是2020-12-09 08:00:00
• 這時候我們有一臺在零時區的伺服器,連線MySQL,並且把當前連線的時區設定為+00:00,再去查資料庫這條記錄,查到的資料是:2020-12-09 00:00:00,正好對應零時區的時間,這樣子我們就不用考慮時區的問題.

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