Mysql中的primary key 与auto_increment

mysql> create table cc(id int auto_increment);
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be def
ined as a key
mysql> create table cc(id int auto_increment primary key);
Query OK, 0 rows affected (0.03 sec)

mysql> desc cc;
+-------+---------+------+-----+---------+----------------+
| Field | Type    | Null | Key | Default | Extra          |
+-------+---------+------+-----+---------+----------------+
| id    | int(11) | NO   | PRI | NULL    | auto_increment |
+-------+---------+------+-----+---------+----------------+
1 row in set (0.01 sec)

mysql>

mysql> create table abc(id int primary key);
Query OK, 0 rows affected (0.04 sec)

mysql>

 

注意：

自动编号Auto_INCREMENT必须与主键PRIMARY KEY组合使用

primary key可以独自使用