when sync to mysql, data may not consitent with timestamp data type if explicit_defaults_for_timestamp var diffreent

[july2993]

in tidb will like this explicit_defaults_for_timestamp is on as default

mysql> create table tm(id int auto_increment, t_timestamp TIMESTAMP, primary key(id));
Query OK, 0 rows affected (0.24 sec)

mysql> show create table tm;
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                        |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tm    | CREATE TABLE `tm` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `t_timestamp` timestamp NULL DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin |
+-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

mysql> insert into tm(t_timestamp) values(null);
Query OK, 1 row affected (0.13 sec)

mysql> select * from tm;
+----+-------------+
| id | t_timestamp |
+----+-------------+
|  1 | NULL        |
+----+-------------+
1 row in set (0.01 sec)

in mysql if explicit_defaults_for_timestamp is off will like this
for mysql Default Value is ON(>= 8.0.2) or OFF(<= 8.0.1)

mysql> create table tm(id int auto_increment, t_timestamp TIMESTAMP, primary key(id));
Query OK, 0 rows affected (0.03 sec)

mysql> show create table tm;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                    |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tm    | CREATE TABLE `tm` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `t_timestamp` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> insert into tm(t_timestamp) values(null);
Query OK, 1 row affected (0.00 sec)

mysql> select * from tm;
+----+---------------------+
| id | t_timestamp         |
+----+---------------------+
|  1 | 2018-05-31 12:55:51 |
+----+---------------------+
1 row in set (0.01 sec)

about explicit_defaults_for_timestamp