MySql 主键自动增长

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    mysql> alter table user modify id integer auto_increment ;      Query OK, 1 row affected (0.28 sec)      Records: 1  Duplicates: 0  Warnings: 0

给主键增加一个自增的功能：

  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)

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>

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