为什么 MySQL 在使用 FROM_UNIXTIME 时计算出错误的时间戳

Question

为什么 MySQL 在使用 FROM_UNIXTIME 时计算出错误的时间戳

Joe*_*ner 6 mysql timestamp timezone

我已经调试了很多，最后设法在 mysql shell 中重现它。

我将时间戳存储在字段类型为的 mysql 数据库中timestamp。我用来FROM_UNIXTIME()从我的脚本中更新它们，并UNIX_TIMESTAMP()在选择它们时使用。

当我没有在使用SET time_zone =它的连接中设置时区时，它工作正常。但是当我设置时区时，会发生以下情况：

UNIX_TIMESTAMP() 仍然给出正确的结果。
UPDATE table SET field = FROM_UNIXTIME(..) 在数据库中设置错误的值。
设置的错误值，与服务器时区和连接时区之间的偏移量不对应。服务器时区为亚洲/曼谷 (UTC + 7)，连接时区为欧洲/柏林 (UTC + 1)。但是，该值以 1 小时的差异存储，而不是 6 小时。
再次读取该值时，我得到了错误的值。

我知道是 FROM_UNIXTIME() 不起作用，因为当我打开另一个没有连接特定时区的连接时，我看到错误的值，直到我再次更新它。

它是 1 小时的差异这一事实让我认为这可能是夏令时问题。因为柏林有夏令时而曼谷没有（据我所知）。

这是 mysql shell 的未修改日志，我在其中重现了此行为。

服务器时区是亚洲/曼谷（CIT）

$ mysql -uroot -p timezonetest
Enter password: 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 530
Server version: 5.7.16-0ubuntu0.16.10.1 (Ubuntu)

Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> SELECT @@system_time_zone;
+--------------------+
| @@system_time_zone |
+--------------------+
| ICT                |
+--------------------+
1 row in set (0.00 sec)

mysql> describe test;
+------------+-----------+------+-----+-------------------+-----------------------------+
| Field      | Type      | Null | Key | Default           | Extra                       |
+------------+-----------+------+-----+-------------------+-----------------------------+
| payment_id | int(11)   | NO   | PRI | NULL              | auto_increment              |
| begins_at  | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+------------+-----------+------+-----+-------------------+-----------------------------+
2 rows in set (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 08:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql> select unix_timestamp(begins_at) from test where payment_id = 338840;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382836533 |
+---------------------------+
1 row in set (0.00 sec)

mysql> set time_zone = 'CET';
Query OK, 0 rows affected (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 02:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql> select unix_timestamp(begins_at) from test where payment_id = 338840;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382836533 |
+---------------------------+
1 row in set (0.00 sec)

mysql> update test set begins_at = from_unixtime(1382836533) where payment_id = 338840;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select unix_timestamp(begins_at) from test where payment_id = 338840;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382832933 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 02:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql>

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另一个日志：

    mysql> describe test;
+------------+-----------+------+-----+-------------------+-----------------------------+
| Field      | Type      | Null | Key | Default           | Extra                       |
+------------+-----------+------+-----+-------------------+-----------------------------+
| payment_id | int(11)   | NO   | PRI | NULL              | auto_increment              |
| begins_at  | timestamp | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+------------+-----------+------+-----+-------------------+-----------------------------+
2 rows in set (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 02:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql> set time_zone = 'Europe/Berlin';
Query OK, 0 rows affected (0.00 sec)

mysql> select unix_timestamp(begins_at) from test;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382832933 |
+---------------------------+
1 row in set (0.00 sec)

mysql> update test set begins_at = from_unixtime(1382836533);
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

mysql> select unix_timestamp(begins_at) from test;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382832933 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 02:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql> set time_zone = 'Asia/Bangkok';
Query OK, 0 rows affected (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 07:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql> select unix_timestamp(begins_at) from test;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382832933 |
+---------------------------+
1 row in set (0.00 sec)

mysql> update test set begins_at = from_unixtime(1382836533);
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select unix_timestamp(begins_at) from test;
+---------------------------+
| unix_timestamp(begins_at) |
+---------------------------+
|                1382836533 |
+---------------------------+
1 row in set (0.00 sec)

mysql> select * from test;
+------------+---------------------+
| payment_id | begins_at           |
+------------+---------------------+
|     338840 | 2013-10-27 08:15:33 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql>

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Answer 1

Mic*_*bot 8

MySQL 运行正常 – 您的测试无效。

如果您使用 DST 来回穿越时区，则在遇到转换时将不会进行无损转换。有问题的时间戳发生在“CET”和“Europe/Berlin”的 DST 转换期间。

亚洲/曼谷有两个挂钟时间对应于欧洲/柏林的一个挂钟时间。

mysql> SELECT CONVERT_TZ('2013-10-27 08:15:33','Asia/Bangkok','Europe/Berlin');
+------------------------------------------------------------------+
| CONVERT_TZ('2013-10-27 08:15:33','Asia/Bangkok','Europe/Berlin') |
+------------------------------------------------------------------+
| 2013-10-27 02:15:33                                              |
+------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT CONVERT_TZ('2013-10-27 07:15:33','Asia/Bangkok','Europe/Berlin');
+------------------------------------------------------------------+
| CONVERT_TZ('2013-10-27 07:15:33','Asia/Bangkok','Europe/Berlin') |
+------------------------------------------------------------------+
| 2013-10-27 02:15:33                                              |
+------------------------------------------------------------------+
1 row in set (0.00 sec)

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将其转换为 UTC 进行检查...

mysql> select convert_tz('2013-10-27 02:59:59','Europe/Berlin','UTC');
+---------------------------------------------------------+
| convert_tz('2013-10-27 02:59:59','Europe/Berlin','UTC') |
+---------------------------------------------------------+
| 2013-10-27 00:59:59                                     |
+---------------------------------------------------------+
1 row in set (0.00 sec)

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两秒后……

mysql> select convert_tz('2013-10-27 03:01:01','Europe/Berlin','UTC');
+---------------------------------------------------------+
| convert_tz('2013-10-27 03:01:01','Europe/Berlin','UTC') |
+---------------------------------------------------------+
| 2013-10-27 02:01:01                                     |
+---------------------------------------------------------+
1 row in set (0.00 sec)

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……一小时两秒后。

或者，翻转它。

mysql> SET @@time_zone = 'CET';

mysql> SELECT FROM_UNIXTIME(1382825733) AS zero,  
              FROM_UNIXTIME(1382825733 + 3600) AS one, 
              FROM_UNIXTIME(1382825733 + 3600 + 3600) as two, 
              FROM_UNIXTIME(1382825733 + 3600 + 3600 + 3600) as three,
              FROM_UNIXTIME(1382825733 + 3600 + 3600 + 3600 + 3600) as four;
+---------------------+---------------------+---------------------+---------------------+---------------------+
| zero                | one                 | two                 | three               | four                |
+---------------------+---------------------+---------------------+---------------------+---------------------+
| 2013-10-27 00:15:33 | 2013-10-27 01:15:33 | 2013-10-27 02:15:33 | 2013-10-27 02:15:33 | 2013-10-27 03:15:33 |
+---------------------+---------------------+---------------------+---------------------+---------------------+
                                                         ^^ ... wait, what? .. ^^
1 row in set (0.00 sec)

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如果您在过渡时间内对不明确的值进行时区转换，则转换不是无损的。

时间戳的操作需要是 UTC 端到端的。在一侧或另一侧使用FROM_UNIXTIME()或UNIX_TIMESTAMP()使用本机 UTC 值，但该值仍会在另一侧转换为您的会话时区（或服务器时区，如果未设置会话时区） - 在成为或从TIMESTAMP列中的值的方式（实际上存储为 UTC，并转换为/从您的会话时区）。

这是您的服务器时钟应始终使用 UTC 的原因之一。

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