![]() ![]() Let’s see how to define a foreign key in a physical model. ERDs include all the information necessary to construct a database as such, they let us define foreign keys. Vertabelo enables us to create ER diagrams easily. Now we’re ready to move on to defining a foreign key in a physical model. Here, this shared column is the AuthorId column. To summarize, the foreign key constraint in a physical model joins the tables on a shared column(s). Foreign keys let us divide data into tables and then link these tables. Otherwise, our data would all be stored in one table, like this: The information about authors is stored in the Authorstable, not in the Books table. Please note that the AuthorId column in Books can use only the values present in the AuthorId column of Authors, as Authors is the primary table. You can trace the AuthorId column to the Authors table to fetch information about the author. ![]() The Books table assigns an author to each book using the AuthorId column. In the Books table (a foreign table), the AuthorId column is a foreign key ( FK). In the Authors table, which is a primary table, the AuthorId column is a primary key (PK). The Books and Authors tables share the AuthorId column. The line between them signifies that one author can have one or more books, but one book can have only one author. ![]() The two tables presented above store information about books and authors. This link is based upon a column shared by these tables. Finally, I’ll show you how to fetch the SQL code of the physical model from Vertabelo.Ī foreign key creates a link between two tables. You’ll also see how vital the foreign key concept is for joining the tables. We’ll discuss the difference between candidate keys, primary keys, and alternate keys so you can understand which one to use as a reference column. Next, we’ll dive into the details of defining a foreign key in a physical model of the database. First, we’ll briefly go over foreign key basics. This article focuses on the concept of the foreign key in a physical model. It facilitates the process of linking the tables. That’s where the foreign key comes into play. You don’t store all your data in one table, but many different tables. A foreign key is one of the fundamental concepts of relational databases. ![]()
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