oreign key constraints (also known as referential constraints or referential integrity constraints) enable you to define required relationships between and within tables. For example, a typical foreign key constraint might state that every employee i…

ntroduction to MySQL foreign key A foreign key is a field in a table that matches another field of another table. A foreign key places constraints on data in the related tables, which enables MySQL to maintain referential integrity. Let’s take a look…

InnoDB表中中Foreign Key定义 1. InnoDB允许a foreign key引用一个索引列或者索引组列. 2. InnoDB现在并不支持用户定义的分区表有foreign keys,这意味着不包含用户定义的分区表InnoDB可以包含foreign key引用,或者被foreign keys引用的列. 3. InnoDB允许a foreign key constraint引用一个non-unique的key,这是对标准SQL的扩展 Foreign Key引用行为 1. SET DE…

Database Primary key and Foreign key --Create Referenced Table CREATE TABLE Department ( DeptID int PRIMARY KEY, --define primary key Name varchar (50) NOT NULL, Address varchar(100) NULL ) --Create Referencing Table CREATE TABLE Employee ( EmpID int…

之前在项目中遇到了这样一个问题,我举得简单的样例来说明. 比方我们有两个表,一个表(department)存放的是部门的信息,比如部门id,部门名称等:还有一个表是员工表(staff),员工表里面肯定要存放每一个员工所在的部门. 那问题来了,假设我们这个时候删除了部门表中的某条记录,在staff表中会发生什么? 为了解答上面的问题,让我们先来回想一下什么是參照完整性. 我们经常希望保证在一个关系中给定属性集上的取值也在还有一个关系的特定属性集的取值中出现.这样的情况称为參照完整性(referen…

主键:一个表中只有一个主键约束,但是一个主键约束可以由数据表中的多个列组成:primary key alter table TName add constraints pk_name PRIMARY KEY (column_name); alter table TName drop constraint pk_name; 外键:数据关联:在一个表中可以有多个.foreign key alter table 设置外键的表 add  constraint fk_name foreign key (n…

Is it bad to rely on foreign key cascading? I'll preface前言 this by saying that I rarely delete rows period. Generally most data you want to keep. You simply mark it as deleted so it won't be shown to users (ie to them it appears deleted). Of course i…

A primary key is defined as a column or a group of column that their value are always be unique. Normally, NULL value will never be allowed in this column to be part of this column’s records. EXAMPLE : Let’s say we want to create a table name Users.…

在stackoverflow找到答案: DATABASES = { 'default': { ... 'OPTIONS': { "init_command": "SET foreign_key_checks = 0;", }, } } (According to the official doc) In previous versions of Django, fixtures with forward references (i.e. relations to r…

http://sevenseacat.net/2015/02/24/add_foreign_key_gotchas.html https://robots.thoughtbot.com/referential-integrity-with-foreign-keys 保证数据库级别参照完整性 `add_foreign_key` gotchas in Rails 4.2 Feb 24, 2015 | Programming, Rails Rails 4.2 finally added native…