Mysql主键自动增长

mysql> create database ssh2;

Query OK, 1 row affected (0.04 sec)



mysql> use ssh2;

Database changed





mysql> create table user(

    -> id integer primary key,

    -> firstname varchar(200) not null,

    -> lastname varchar(200) not null,

    -> age integer

    -> );

Query OK, 0 rows affected (0.46 sec)

 

给主键增加一个自增的功能：

mysql> alter table user modify id integer auto_increment ;

Query OK, 1 row affected (0.28 sec)

Records: 1  Duplicates: 0  Warnings: 0

 

这样，上面的user表里面的主键，id可以自增了。

给上面的主键id增加默认值和自增功能。

mysql> alter table user modify id integer default '1';

Query OK, 0 rows affected (0.16 sec)

Records: 0  Duplicates: 0  Warnings: 0



mysql> alter table user modify id integer auto_increment ;

Query OK, 1 row affected (0.28 sec)

Records: 1  Duplicates: 0  Warnings: 0

MySql获取系统时间：

mysql> alter table user add createtime timestamp default current_timestamp;

Query OK, 2 rows affected (0.17 sec)

Records: 2  Duplicates: 0  Warnings: 0

 

MySql设置主键不能为空，还要自动增长（这里没有设置默认值，但是默认是1，从1开始增长。），还要得到系统默认日期：

mysql> create table dd(

    -> id int primary key not null auto_increment,

    -> name varchar(20),

    -> time timestamp default current_timestamp

    -> );

Query OK, 0 rows affected (0.10 sec)



mysql> insert into dd(name) values ('fhihgifds');

Query OK, 1 row affected (0.14 sec)



mysql> insert into dd(name) values ('steven');

Query OK, 1 row affected (0.08 sec)



mysql> select * from dd;

+----+-----------+---------------------+

| id | name      | time                |

+----+-----------+---------------------+

|  1 | fhihgifds | 2011-03-27 01:58:46 |

|  2 | steven    | 2011-03-27 01:59:35 |

+----+-----------+---------------------+

2 rows in set (0.08 sec)



mysql> insert into dd(name) values ('anthony');

Query OK, 1 row affected (0.09 sec)



mysql> select * from dd;

+----+-----------+---------------------+

| id | name      | time                |

+----+-----------+---------------------+

|  1 | fhihgifds | 2011-03-27 01:58:46 |

|  2 | steven    | 2011-03-27 01:59:35 |

|  3 | anthony   | 2011-03-27 02:00:07 |

+----+-----------+---------------------+

3 rows in set (0.00 sec)



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