Summary: How to drop MySQL database tables and recreate them when you have foreign keyrelationships between the tables. This is pretty obscure, but I thought I'd post it here so I wouldn't forget how to do this ... if you ever have a situation when u
Every movie needs a director and every rented movie needs to exist in the store. How do we make sure something in another table exists before inserting new data? This lesson will teach us about foreign keys and references. CREATE TABLE directors ( id
SQL FOREIGN KEY 约束 一个表中的 FOREIGN KEY 指向另一个表中的 PRIMARY KEY. 让我们通过一个例子来解释外键.请看下面两个表: "Persons" 表: Id_P LastName FirstName Address City 1 Adams John Oxford Street London 2 Bush George Fifth Avenue New York 3 Carter Thomas Changan Street Beijing &qu
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
在需要实现级联删除的情况下,使用 FOREIGN KEY的ON DELETE CASCADE选项非常方便,但在同一张表中,如果有两个外键引用外表数据,那么最多只能将一个外键设为 ON DELETE CASCADE,其他的引用约束需要使用触发器实现级联删除. 1 --建立单词表 2 IF EXISTS (SELECT * FROM sysobjects WHERE name='Word') 3 DROP TABLE Word 4 CREATE TABLE Word 5 ( 6 wordID int