我是sql的新手。
当我尝试创建外键时出现此错误:
cannot add foreign key constraint
当我尝试创建ORDERS表时。这是我的代码:
drop database if exists Company;
create database Company;
use Company;
create table WORKERS(w_id varchar(4), w_name varchar(20) not null, telephone varchar(12), e_mail varchar(35) unique);
create table CUSTOMERS(customer_id varchar(4), customer_name varchar(20) not null, telephone varchar(12), e_mail varchar(35) unique, credit bool);
create table WAREHOUSE(m_id int unsigned primary key, describes varchar(20) not null, fl char(1));
create table ITEM(p_id int(4) unsigned primary key, p_name varchar(15) not null, p_price float not null);
create table INVENTORY(in_id int auto_increment primary key, m_id int unsigned not null, p_id int(4) unsigned not null, amount int not null,
foreign key (m_id) references WAREHOUSE(m_id),
foreign key (p_id) references ITEM(p_id)
);
create table ORDERS(o_id int auto_increment primary key, customer_id varchar(4),
p_id int(4) unsigned, w_id varchar(4), amount int unsigned not null,
date_of_order date not null,
foreign key (p_id) references ITEM(p_id),
foreign key (w_id) references WORKERS(w_id),
foreign key (customer_id) references CUSTOMERS(customer_id)
);
我把ORDERS(我有问题的地方)放在不同的行上,以便你阅读。
我在这里搜索答案,但没有找到任何能回答我问题的具体内容。
任何人都知道问题是什么?谢谢!
答案 0 :(得分:1)
问题是,您尝试与FOREIGN KEY
和WORKERS
表格中未设置为CUSTOMERS
的字段创建PRIMARY KEY
关系。
FOREIGN KEY
需要指向PRIMARY KEY
。将您的创建脚本更改为以下内容:
create table WORKERS(w_id varchar(4) primary key, w_name varchar(20) not null, telephone varchar(12), e_mail varchar(35) unique);
create table CUSTOMERS(customer_id varchar(4) primary key, customer_name varchar(20) not null, telephone varchar(12), e_mail varchar(35) unique, credit bool);
但请注意。我建议不要将VARCHAR (4)
用作PRIMARY KEY
字段。我建议改为使用INT AUTO_INCREMENT
。
答案 1 :(得分:1)
引用表的列应声明为primary key
以分配外键。对于您的orders
表,WORKERS(w_id)
和CUSTOMERS(customer_id)
未被声明为主键,因此您会收到错误。
修改后的声明:
drop database if exists Company;
create database Company;
use Company;
create table WORKERS(w_id varchar(4) primary key, w_name varchar(20) not null, telephone varchar(12), e_mail varchar(35) unique);
create table CUSTOMERS(customer_id varchar(4) primary key, customer_name varchar(20) not null, telephone varchar(12), e_mail varchar(35) unique, credit bool);
create table WAREHOUSE(m_id int unsigned primary key, describes varchar(20) not null, fl char(1));
create table ITEM(p_id int(4) unsigned primary key, p_name varchar(15) not null, p_price float not null);
create table INVENTORY(in_id int auto_increment primary key, m_id int unsigned not null, p_id int(4) unsigned not null, amount int not null,
foreign key (m_id) references WAREHOUSE(m_id),
foreign key (p_id) references ITEM(p_id)
);
create table ORDERS(o_id int auto_increment primary key, customer_id varchar(4),
p_id int(4) unsigned, w_id varchar(4), amount int unsigned not null,
date_of_order date not null,
foreign key (p_id) references ITEM(p_id),
foreign key (w_id) references WORKERS(w_id),
foreign key (customer_id) references CUSTOMERS(customer_id)
);