title: mysql time zone: different column value changes after changing time zone
body: <p>MySql: changing time_zone from +00:00 to SYSTEM,
  one time column changed 5 hours, another time column changed 4 hours, vise versa. both are timestamp.</p>
  <pre><code>mysql&gt; desc foo;
  +--------------------+---------------+------+-----+-------------------+----------------+
  | Field              | Type          | Null | Key | Default           | Extra          |
  +--------------------+---------------+------+-----+-------------------+----------------+
  | id                 | bigint(10)    | NO   | PRI | NULL              | auto_increment |
  | time               | timestamp     | NO   |     | CURRENT_TIMESTAMP |                |
  | time1              | timestamp     | NO   |     | CURRENT_TIMESTAMP |                |
  +--------------------+---------------+------+-----+-------------------+----------------+
  4 rows in set (0.00 sec)
  
  
  mysql&gt; select @@time_zone;
  +-------------+
  | @@time_zone |
  +-------------+
  | +00:00      |
  +-------------+
  1 row in set (0.00 sec)
  
  mysql&gt; select id, time, time1 from foo where id=1;
  +----+---------------------+---------------------+
  | id | time                | time1               |
  +----+---------------------+---------------------+
  |  1 | 2021-03-01 05:00:00 | 2021-03-26 04:55:21 |
  +----+---------------------+---------------------+
  1 row in set (0.00 sec)
  
  mysql&gt; set time_zone='system';
  Query OK, 0 rows affected (0.00 sec)
  
  mysql&gt; select id, time, time1 from foo where id=1;
  +----+---------------------+---------------------+
  | id | time                | time1          
  |
  +----+---------------------+---------------------+
  |  1 | 2021-03-01 00:00:00 | 2021-03-26 00:55:21 |
  +----+---------------------+---------------------+
  1 row in set (0.00 sec)
  </code></pre>
  <p>Mysql version: 5.7.11</p>