MySQL遇到的报错信息（截止到7.17）

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1.ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

mysql> create table grades06(
    -> id int not null auto_increment,
    -> name varchar(12) primary key,
    -> grade float default 0);
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key

自增列只能有1列， 且这列必须为key，改后如下：

mysql>  create table grades06(
    ->  id int not null auto_increment primary key,
    -> name varchar(12),
    -> grade float default 0);
Query OK, 0 rows affected (0.02 sec)

2.Multiple primary key defined
定义了多个主键，我们要知道每个数据表最多只能有一个主键约束。
3.Incorrect prefix key; the used key part isn’t a string, the used length is longer than the key part, or the storage engine doesn’t support unique prefix keys
索引中的的长度超出了字段数据类型定义的长度。解决办法是索引中不写长度，或者把长度改到相应的长度以内。
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4.ERROR 1364 (HY000): Field ‘xxxx’ doesn’t have a default value，
字段xxxx为非空约束，不能插入空值。

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