timestamp ---自动更新修改时间 与 记录首次插入时间

自动更新修改时间:

mysql> create table z(a int ,b timestamp on update current_timestamp); 

mysql> insert into z select ,current_timestamp;

mysql> select * from z;
+------+---------------------+
| a    | b                   |
+------+---------------------+
|     | -- :: |
+------+---------------------+
 row in set (0.00 sec)

mysql> insert into z select ,current_timestamp;
Query OK,  row affected (0.18 sec)
Records:   Duplicates:   Warnings: 

mysql> select * from z;
+------+---------------------+
| a    | b                   |
+------+---------------------+
|     | -- :: |
|     | -- :: |
+------+---------------------+
 rows in set (0.00 sec)

mysql> update z set a=a+ where a=;
Query OK,  row affected (0.20 sec)
Rows matched:   Changed:   Warnings: 

mysql> select * from z;
+------+---------------------+
| a    | b                   |
+------+---------------------+
|   | -- :: |
|     | -- :: |
+------+---------------------+
 rows in set (0.00 sec)

记录首次插入时间:

mysql> create table x (a int, b timestamp default current_timestamp);
Query OK,  rows affected (0.22 sec)

mysql> select * from x;
Empty set (0.00 sec)

mysql> insert into x(a) values();
Query OK,  row affected (0.18 sec)

mysql> select * from x;
+------+---------------------+
| a    | b                   |
+------+---------------------+
|     | -- :: |
+------+---------------------+
 row in set (0.00 sec)

mysql> insert into x(a) values();
Query OK,  row affected (0.19 sec)

mysql> select * from x;
+------+---------------------+
| a    | b                   |
+------+---------------------+
|     | -- :: |
|     | -- :: |
+------+---------------------+
 rows in set (0.00 sec)