MySQL中的主键以及设置其自增的用法教程

mysql> alter table user modify id integer auto_increment ;

Query OK, 0 rows affected (0.39 sec) Records: 0 Duplicates: 0 Warnings: 0

 

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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