mySQL 中主鍵值自動增長

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

 

MySql 主鍵自動增加

博客分類：

 
• DataBase

MySQL SQL 

建立數據庫，建立表。 

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)

給主鍵增長一個自增的功能： 

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

這樣，上面的user表裏面的主鍵，id能夠自增了。 









給上面的主鍵id增長默認值和自增功能。 

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獲取系統時間： 

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設置主鍵不能爲空，還要自動增加（這裏沒有設置默認值，可是默認是1，從1開始增加。），還要獲得系統默認日期： 

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>