#在创建完表后,修改自增字段的起始值 mysql> create table student( -> id int primary key auto_increment, -> name varchar(20), -> sex enum('male','female') default 'male' -> ); mysql> alter table student auto_increment=3; mysql> show create table student; ... ENGINE=InnoDB AUTO_IN...
create table t3 (id int primary key auto_increment, name varchar(20)); #创建一个server表 设置ip和port 为主键列 这2个列为and关系 这ip和port不能同时有重复数据 create table server(ip varchar(15), port char(5), server_name varchar(10) not null,primary key(ip,port)); 表基本修改操作 #...
constraint fk_book foreign key(book_id) references book(id) on delete cascade on update cascade, primary key(author_id,book_id)); insert into author(name) values('Alex'),('Coco'),('BeiBei'),('Python'); insert into author2book(author_id,book_id) values (1,1),(1,2),(1,3),(1...
它有一个或多个作者(和作者是多对多的关联关系[many-to-many]), 只有一个出版商(和出版商是一对多的关联关系[one-to-many],也被称作外键[foreign key]) 它说,书籍和出版商的关系是一对多,OneToMany(也叫外键,ForeignKey),这个我就觉得没法理解,在我看来,一本书应该只能属于一个出版商,一个出版商可以出多本...
这是因为MySQL中设置了foreign key关联,造成无法更新或删除数据。 解决方法: 可以通过设置FOREIGN_KEY_CHECKS避免这种情况。 执行SET FOREIGN_KEY_CHECKS=0;禁用外键约束。删除数据后可以在开启外键约束:SET FOREIGN_KEY_CHECKS=1;比如: 代码语言:javascript
2,child model :foreign key 注释掉,执行makemigratios,migrate(删掉外键) 3,child model :foreign key 注释解除,执行makemigratios,migrate(追加外键) 詳細: parent変更前:python manage makemigrations parent app 実施時、自動追加 primary key「id」
MySQL允许我们在表中的多个字段上添加FOREIGN KEY约束。唯一的条件是,子表中每个外键必须引用不同的父表。 阅读更多:MySQL 教程 示例 假设我们有一个名为’customer2’的表,它在字段’cust_unq_id’上有一个主键约束,如下所示: mysql>describe customer2;+---+---+---+---+---+---+...
TheFOREIGN KEYconstraint is used to prevent actions that would destroy links between tables. AFOREIGN KEYis a field (or collection of fields) in one table, that refers to thePRIMARY KEYin another table. The table with the foreign key is called the child table, and the table with the prima...
in the table and is always unique, such as a student’s ID card number. Such a key is called anatural key. However, it is also a common practice to use asurrogate keyinstead. A surrogate key is not part of the actual data; its only purpose is to be a unique row identifier within...
Updated Sep 25, 2020 Python k1LoW / tmpfk Star 6 Code Issues Pull requests Temporary foreign key add/drop tool for using ERD generator for "Keyless entry (SQL Antipatterns)" schema. activerecord cakephp foreign-keys ruby-on-rails Updated Feb 27, 2017 Ruby aj...