Table of Contents
Where should the foreign key be placed in a one to one relationship?
(See the subtypes tag). The second problem is the one-to-one relationship between Persons and Users. If you just had a Persons table, then the question of which way the foreign keys should go is driven by the fact that the relationship is mandatory at one end, but optional at the other end.
Is the custid in the Order table a foreign key?
In our Case, CustID in the Customer table is Primary or Unique Key. At the same time, the CustID in the Order table is a Foreign Key which refers the column CustID in the Customer table. Note, if we designed the One-to-Many Relation between two tables, then Many-To-One relation results automatically.
Can a single parent have two foreign keys?
There will still be cases where some of these relationships exist and sometimes they don’t. That’s the reality of your business rules. There’s a difference, however between having two mutually exclusive foreign keys in one table and having multiple optional relationships to a single parent. – Joel Brown Feb 7 ’16 at 14:34
Why do I need a double FK key?
Your current design (with the double FK in users) both permits the modelling of the fields you need for each different type, and allows you to have the (desirable?) mutual exclusivity to prevent a user from being both a customer and an employee.
When do you use the FOREIGN KEY constraint?
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
What is the purpose of the restkit framework?
It provides a powerful object mapping engine that seamlessly integrates with Core Data and a simple set of networking primitives for mapping HTTP requests and responses built on top of AFNetworking. It has an elegant, carefully designed set of APIs that make accessing and modeling RESTful resources feel almost magical.
Which is the parent table with the foreign key?
A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table. The table with the foreign key is called the child table, and the table with the primary key is called the referenced or parent table. Look at the following two tables:
What is a foreign key in SQL Server?
A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table. The table containing the foreign key is called the child table, and the table containing the candidate key is called the referenced or parent table.