mySQL 中主键值自动增加

转  http://stevenjohn.iteye.com/blog/976397

 

MySql 主键自动增长

博客分类：

 
• DataBase

MySQLSQL 

创建数据库，创建表。 

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 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)

mysql>