Hey, everyone. Welcome, welcome. Lovely to see you here as we continue our adventures in topic one of our database class. In this video, part five, we're going to focus on the purpose and value of the structured query language. This structure query language on its own will constitute the entire third topic in our class. And this is, in my opinion, the most valuable skill that you can take away from this class. To being able to understand work with and write effective queries using the structured query language. The reason why one of the reasons why is that it is a standardized language. That is supported by all major relational database vendors. So if you can learn this once, what that means is that you can use any major database on the market. It doesn't matter if it's SQL Server, MySQL, DB2 oracle. You would be able to sit down at any of those databases and start doing work immediately with essentially no additional learning curve. Of course, I'm simplifying things a little bit, but general principle holds. If you can learn this once, you can use it on any different standardized database environment. Further, the vast majority of the data driven apps that are out there now on mobile phones, tablets, desktop apps, web based apps, the vast majority of them are using SQL, the structured query language on the back end. In order to save update, delete and retrieve information on behalf of the users. So it's not just human beings that rely on these SQL statements. But the apps that are such a central part of our lives now are also using SQL. It's hidden from us as users, but they are sending SQL requests to lots of databases. It could be a web based database, something that lives locally like on a desktop machine or something that lives, say on your mobile phone. So learning SQL is an extraordinarily valuable skill. As we'll see when we take a look at SQL as a standalone topic, it is in extraordinarily high demand right now as well. What I wanted to do was show you that even if you have never seen or written any structured query language statements before that with just a little bit of effort, you can understand what's happening. These statements are written in such a way as to use simple English language terms and to be relatively intuitive. For our sample example, let's say that we have a database, this is an art course database here, where we have three different tables. And we're going to see a SQL statement that can pull information from these tables. So in this case, I have store information about my customers up here and I have information about the various art courses that I make available here. And the enrollment table keeps track of which customers have enrolled in which art class and how much they've paid to our little art company. So simple little database design just keeping track of which customers are taking which art classes. And let's see a sample SQL statement. So if you wanted to pull information from all three of those tables generate some kind of report, we could do that by writing a SQL select statement. So let's just see a quick example here. Now I know at first glance this looks big and complicated, but if you look a little more closely, you'll see that it's really not that scary. So the first is the keyword select and following that keyword, we just list all of the things that we want to appear in the results. So what we're saying here is what I want to appear in the results is the first last name, customers first name phone number, the date of the course that customer is taking. that the customer has paid, this would be like a name of the class and the total fee for taking the class. So maybe the customer has only paid a down payment on the total fee. So those are the things that we want to appear in the results easy enough. And then the next thing we have to do in this example is tell the database where it needs to look in order to get all this information. So in this case, we have to pull information from the customer table, right, because we have information about customers. We have to pull additional information from the enrollment table, because we have some information about enrollments that we want to retrieve as well. And we need to pull information from a third table, a course table in this case, because we have information about courses. That we are also interested in. So thus far it's just here's what we want in the results. Here's where you need to look for it. And then we just need to tell the database to how to link these three tables together. And again, in the relational database world, we do that using matched pairs of values. So we tell the database, hey, the customer number in the customer table needs to match the customer number and the enrollment table. And the course number in the course table needs to match with the course number in the enrollment table. So we're telling you how to link all of these things together. And then that's all we need to do with the database will go out and do all the work for us and give us the results. So my hope is that even now, if you've never seen or written any SQL statements before on our first topic of our database class, you can look at this and get a sense of what's happening. It just uses a lot of simple English language words select from where and it's nothing that's terribly complicated here it's much much simpler than, for example, trying to learn programming language. And then this statement might give us some results that look a little something like this. So in this case, we're generating some sort of report and you'll note here that the output. The customer's last name first name phone number core state amount paid name of the course and the fee total course fee. Right, that corresponds directly to the order. And which we requested that information out of the database, we requested the customers last name and then the first name and then the phone number and then the core state amount paid course name and fee and so on. And that's exactly what we got after this ramp in that order.