What is a Foreign Key Constraint? Understanding Primary & Foreign Keys

In this short video we'll cover what foreign keys are, why they are important, how they differ from Primary Keys and how they function in a relational database.

00:00 Introduction
0:21 Example of Foreign Keys in a database
0:32 What is a Primary key?
1:19 What is a foreign key?
2:02 What do foreign keys do?
3:27 Review of Foreign Keys

In this video, we are focusing on foreign keys that link one column in a table to one column (the primary key) in another table for the sake of simplicity. Your own use of a foreign key can be more complex: foreign keys can link to a compound (more than one column) in another table, and foreign keys do not have to link to another table's primary key.

Just keep in mind that whatever your foreign key is referencing in the other table must have a unique constraint (this is why using a foreign key to reference another table's primary key is often a good idea, since we know that has a unique constraint by default).

#ForeignKeys #PrimaryKeys #RelationalDatabase #CockroachDB

[hristohristov]

Very well explained and clearly illustrated. And I mean it!

[xskftxm]

Thank you for such a comprehensive way of presenting the information!

[msingh]

Best lecture to clear key confusions arising from definitions.

[rira]

Well explained, Impressive illustrated 🤝Good job

[bradleyli]

Concise and comprehensive explanation! Thanks very much!

[purpledragon]

Thank you! I couldn't understand this concept from the Coursera course I'm taking. Your video effectively cleared my confusion!

[shukes]

it took me at least 30 minutes to find an understanding video. That doesn't have an overly thick uninteresting indian guy making 0 sense. And i finally found someone who explains it in under 10 minutes and is short, simple and awesome. Thank you very much

[igorg.]

Is there a way to use this concept to avoid duplicating data across tables? For example - there is an Orders table and a MyOrders table. I'd like MyOrders table to automatically reference Orders without duplicating the data in it....

[-.-_._--]

Great but is it also possible that a column is both a primary key and foreign key in the same table

[senju]

So it's not possible to insert data only into a parent table without having an error?