mysql 约束条件 auto_increment 自动增长 修改自增字段起始值

 

 

创建一张表 t20

mysql> create table t20( id int primary key auto_increment, name char(16) );
Query OK, 0 rows affected (0.01 sec)

mysql> desc t20;
+-------+----------+------+-----+---------+----------------+
| Field | Type     | Null | Key | Default | Extra          |
+-------+----------+------+-----+---------+----------------+
| id    | int(11)  | NO   | PRI | NULL    | auto_increment |
| name  | char(16) | YES  |     | NULL    |                |
+-------+----------+------+-----+---------+----------------+
2 rows in set (0.00 sec)

 

修改自增字段为3 下次插入新纪录 从3开始

mysql> alter table t20 auto_increment=3;
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show create  table t20\G;
*************************** 1. row ***************************
       Table: t20
Create Table: CREATE TABLE `t20` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(16) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

 

插入记录

mysql> insert into t20(name) values('mike');
Query OK, 1 row affected (0.00 sec)

mysql> select * from t20;
+----+------+
| id | name |
+----+------+
|  3 | mike |
+----+------+
1 row in set (0.00 sec)

 

 

mysql> show create  table t20\G;
*************************** 1. row ***************************
       Table: t20
Create Table: CREATE TABLE `t20` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` char(16) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8
1 row in set (0.00 sec)