One to Many Relationship is a free tutorial by Rares Ilea from Database Design course
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Course summary:
Learn what a database is
Learn how databases work and why are they important
Learn data modeling and the 3 levels of relational database design
Learn what are the steps to create a sound database design
Learn what database normalization is and how to apply 1NF, 2NF and 3FN in database design
Learn how to build database relationships: one-to-one, many-to-one and many-to-many
Understand better every theoretical step by following several concrete examples
You will be able to design a relational database from scratch
You will be able to answer the most common interview questions about databases
You will have a concrete e-commerce database design schema to add to your portofolio
English [Auto]
Hi and welcome back in this lecture I show you a few examples of one to many relationships and one to many relationship allows a single record in one table to be related to multiple records in another table. And this is one of the most commonly used type of relationships. So let's see an example from our database. Let's look at the relationship between products and brands. As you can see in the example one or more products belong to our brand. That means that between products and brands there is a many to one relationship. If you look the other way around there is a one to many relationship between brands and products or in other words or brand has many products. Basically the one thing you should note here is that one too many and many to one is the same relationship. Nothing changes in the D-B. It just depends from which side you look at it. OK. That being said before we move to our next example let's update that design in my sequel workbench. Now before I create the relationship between products and brands I want to discuss about the brands primary key so even if we could use the brand name as the primary key in the brand stable because no two brands have the same name I'll add them ID column of type and which would be our number. Why is that. Well in most web applications it is easier to work with IDS which have numbers and on a second thought we do our small size optimization. Imagine that you have 1000 iPhones in your store and for every one of them you have to specify the foreign key to the brand as the word apple instead of a number like one. Obviously that will take much more storage. So I'll go ahead and create the ID column of type and set it as the primary key and I'll remove the brand as the primary key and move the primary key as being the first column and then replace the brand name wait name. Simple as that. OK. And now let's create the relationship. So I'll choose a one to many relationship and click on the product and then on the brand's and that's it the relationship has been created. And as you can see my sequel added by default brands ID foreign key in the products table. Now what do I remove the brand. Column from here since it has been replaced with the brands ID for on key and we are done. Now let's move on with our examples. Imagine the product stable as it is now. We are using some assign IDs for our products. Considering that every product in the world has an unique serial number. Do you think we could use that in place of our ID. Of course we can and probably everything will become better integrated with the cash register. To make up around Tiss for mobile phones the serial number is called I mean a code and you can find it on their backs or on their menu and using it you can verify the phones out in the city. Let's use that as the ID OK. Now let's add a few more products to our table. Imagine you have in your store the iPhone 7 you could as well have 1000. Do you see some data redundancy here. In other words repeating data Well the name tag line description price brand and warranty are repeating for every product. As you can see for the iPhone 7 we should remove that data redundancy from our design. So how could we do that. You may as well imagine that every product we have is actually a physical item with an unique serial number the name description brand etc. are attributes that are the same for each item and represent the product. In our case iPhone 7 they could be extracted in some other table. Think for a moment how would you do that. Ready Let me show you how I would break these data in two tables. One is called products and store genetic data about the product and the other is called item here we store specific item related data. There's no relationship between products and items is a one to many relationship a

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