By Richard Rost 3 years ago
Relating Multiple Tables, One-to-Many, et al.
In this video you will learn about relationships in Microsoft Access. You will learn how to relate data from different tables together, and why it's important for good database design.
Simone from Bridgeport, Connecticut (a Platinum Member) asks: I'm a realtor. I'm in the process of setting up my first Access database. I've been using Excel for years to track my customers and the houses they've purchased. Once in a while I get a customer who has purchased multiple houses. Should I make a separate entry for each of them in my customer table? It seems like this would be an awful lot of duplicated data.
Members will learn about Self Joins, Global Relationships, and Referential Integrity which is where you can prevent entry of a child record without a matching parent record, or delete a parent if it has children. We'll also talk about cascade updates and deletes and why I personally don't use them.
Silver Members and up get access to view Extended Cut videos, when available. Gold Members can download the database template from class plus get access to the Code Vault. If you signed up on YouTube you have to register on my YouTube Find User page so I can set up your account here on my web site. If you're not a member, Join Today!
Relating your tables together is the fundamental backbone of building databases. It's what separates "modern" databases like Access from spreadsheets and "flat-file" databases of years gone by.
Essentially, you want to make multiple tables in your databases to cut down on duplicate data. Duplicate data slows your database down and makes it inefficient (not to mention cumbersome to update and edit). Imagine having to store every customer's information with every order they place! Not too efficient.
So you make multiple tables, and you relate them to each other - usually with an ID or "key" field. For example, in this screenshot from my class, I'm showing students how to create two tables to relate drivers and vehicles. By moving the driver data to a different table, we've created a properly "normalized" database. Normalization is key to a good database.
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