[英]Auto increment column
I want to make an AUTO_INCREMENT column in a database table,here is the syntax i write: 我想在数据库表中创建一个AUTO_INCREMENT列,这是我写的语法:
create table comments
(
name varchar(20),
mail varchar(30),
comment varchar(100),
com_no int auto_increment
);
and i get the following error: 我得到以下错误:
ERROR 1075 (42000): Incorrect table definition; 错误1075(42000):错误的表格定义; there can be only one auto column and it must be defined as a key 只能有一个自动列,并且必须将其定义为键
then i made it as a primary key: 然后我将其作为主键:
create table comments
(
name varchar(20),
mail varchar(30),
comment varchar(100),
com_no int primary_key auto_increment
);
and i get the following error: 我得到以下错误:
ERROR 1064 (42000): You have an error in your SQL syntax; 错误1064(42000):您的SQL语法有错误; check the manual that corresponds to your MySQL server version for the right syntax to use near 'primary_key auto_increment,name varchar(20),mail varchar(30),comment varchar(100' at line 1 检查与您的MySQL服务器版本相对应的手册以获取正确的语法,以在第1行的'primary_key auto_increment,name varchar(20),mail varchar(30),comment varchar(100')附近使用
what is wrong??? 怎么了???
It is PRIMARY KEY
without the underscore. 它是没有下划线的PRIMARY KEY
。
create table comments
(
name varchar(20),
mail varchar(30),
comment varchar(100),
com_no int primary key auto_increment
);
or 要么
create table comments
(
name varchar(20),
mail varchar(30),
comment varchar(100),
com_no int auto_increment,
primary key(`com_no`)
);
create table comments(
name varchar(20),
mail varchar(30),
comment varchar(100),
com_no int auto_increment,
PRIMARY KEY (com_no)
);
(as per on-line MySQL manual). (根据在线MySQL手册)。
使用primary key
代替primary_key
The proper syntax goes like this for example: 正确的语法如下所示:
CREATE TABLE `admin` (
`id` INT(5) UNSIGNED NOT NULL AUTO_INCREMENT,
`userid` VARCHAR(50) NULL DEFAULT '0',
`pwd` VARCHAR(50) NULL DEFAULT NULL,
PRIMARY KEY (`id`)
)
In MySQL , there can be only one auto increment column (that is generally known as identity column ) and it should be also defined as a unique key . 在MySQL中 ,只能有一个自动增量列(通常称为标识列 ),并且还应将其定义为唯一键 。 For example: 例如:
create table comments
(
com_no int NOT NULL AUTO_INCREMENT,
name varchar(20),
mail varchar(30),
comment varchar(100),
PRIMARY KEY (com_no)
);
Please see MySQL auto increment documentation for more details. 请参阅MySQL自动递增文档以获取更多详细信息。
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