Hi, and welcome to this course on SQL databases. In this introductory video, we're going to discuss what a sequel database is. I think one of the best ways of understanding sequel is to understand a little bit about the history of databases to help understand exactly how we got to the point where we're at right now.

So decades ago the way that you would store data in a program is you would write to something called a flat file. A flat file was simply a regular file and every time you got a new record you would append a new record to the end of that flat file. Now doing this allowed you to store and persist your data, meaning that when the program was over you'd be able to still have it there on the system. This had a few issues.

Imagine that you were building a new Twitter and you tried to use a flat file. You'd have some issues because every single time that you created a post and you looked at your feed, you are looking at more than just one type of data element. You may be looking at a tweet but then you also need to know who that tweet belongs to. Which means that you have to have a reference to users, You would also have to have the ability to store how many likes that it got, how many read tweets, and how many responses. There's all kinds of relational data that is there that if you were just trying to keep track of it in a single file or in a single record it would start to get really messy.

That is how we ended up in a situation where we're at right now with SQL databases. SQL gives us the ability to have relational data, and by relational, I mean that you can have all kinds of database tables and you're not limited to a single one. These tables can all have references to each other.

Take our Twitter example again if you have a tweet, that tweet can belong to a user. That tweet will have a reference to the users table. Then you can very quickly go in the Users table and find out which user created it. You can also quickly see how many times it is retweeted by going to a retweet table. You can see how many ‘likes’ there are and you can see who gave the likes.

Instead of building your system on just a single table that contains a huge amount of data with relational type of data. You can create much smaller tables that are all mapped to each other. That's really where the power of SQL databases come in. You can just create very basic types of tables that have the ability to have references to each other. That's how you get the name relational databases.

So you have a good idea on what relationships are. Let's just kind of take a step back and talk about how databases are used. So there are all kinds of applications use databases in modern times and many of them still use SQL databases, even though it's a technology that's been out there for quite a long time. It's still very popular and still continues to grow.

The reason for that is because when you are modeling data it really makes logical sense to be able organize it in a way that SQL does it. So whenever you're logging in to a business application or your banking system. Those are using sequel databases for the most part to be able to store and manage your data.

I am very excited to go through this course with you. We're going to learn all about SQL from the ground up. You don't have to have any prior experience or knowledge about what SQL is we're going to start with the basics and move up through advanced queries. So now that you have a good idea on what databases are, how they're used, and what we're going to be doing in this course. In the next guide we're going to talk about the SQL database types.