Mysql主键自动增长
2012-07-14 20:31
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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) mysql>
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