Default value of TIMESTAMP type in MYSQL _ MySQL

The default value of TIMESTAMP type in MYSQL is bitsCN. in comMYSQL, you can set the default value of TIMESTAMP type, just like other types.
1. Automatic UPDATE and INSERT to Current time:
Table:
-----------
Table Create Table
-------------------------------
T1 create table 'T1 '(
'P _ c' int (11) not null,
'P _ time' timestamp not null default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP
) ENGINE = InnoDB default charset = gb2312
Data:
1 2007-10-08 11:53:35
2 2007-10-08 11:54:00
Insert into t1 (p_c) select 3;
Update t1 set p_c = 2 where p_c = 5;
Data:
1 2007-10-08 11:53:35
5 2007-10-08 12:00:37
3 2007-10-08 12:00:37
2. automatic INSERT to the current time, but not automatic UPDATE.
Table:
-----------
Table Create Table
---------------------
T1 create table 'T2 '(
'P _ c' int (11) not null,
'P _ time' timestamp not null default CURRENT_TIMESTAMP
) ENGINE = InnoDB default charset = gb2312
Data:
Insert into t2 (p_c) select 4;
Update t2 set p_c = 3 where p_c = 5;
1 2007-10-08 11:53:35
2 2007-10-08 12:00:37
5 2007-10-08 12:00:37
4 2007-10-08 12:05:19
3. a table cannot have two Fields. the default value is the current time. Otherwise, an error occurs. But others can.
Table:
-----------
Table Create Table
-----------------------
T1 create table 'T1 '(
'P _ c' int (11) not null,
'P _ time' timestamp not null default CURRENT_TIMESTAMP,
'P _ timew2 'timestamp not null default '2017-00-00 00:00:00'
) ENGINE = InnoDB default charset = gb2312
Data:
1 2007-10-08 11:53:35 0000-00-00 00:00:00
2 12:00:37 0000-00-00 00:00:00
3 2007-10-08 12:00:37 0000-00-00 00:00:00
4 12:05:19 0000-00-00 00:00:00
TIMESTAMP variant
1, timestamp default CURRENT_TIMESTAMP on update CURRENT_TIMESTAMP
This data column is refreshed when a new record is created and an existing record is modified.

2, timestamp default CURRENT_TIMESTAMP
This field is set to the current time when a new record is created, but it will not be refreshed when it is modified later.

3, timestamp on update CURRENT_TIMESTAMP
Set this field to 0 when creating a new record, and refresh it later.

4, timestamp default 'yyyy-mm-dd hh: mm: SS' on update CURRENT_TIMESTAMP
Set this field as a given value when creating a new record, and refresh it later.

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