Original subtitles

‫All right, Querrey time.

‫So in the previous video, we ended on talking about queries, a query is nothing more than an instruction

‫write in English.

‫A query is defined as a question.

‫And Enescu, well, queries are the way that we are going to put together our questions to which we

‫want an answer from the database.

‫A query is also known as an equal statement.

‫Those are just synonyms.

‫Query is equal to ask you all.

‫Statement, as you will statement is equal to a query, just different ways of saying the same thing.

‫So if we look here, there is a very basic query select star from users.

‫And if we were to break this down, what it's basically saying is select us all of the information.

‫So the star here is what we call a wild card.

‫We don't know what we want to get back, but just get us everything back.

‫So select us everything from so we're going to say where we want it from.

‫And we know somewhere in our database we are storing users.

‫Right.

‫So select us everything from users.

‫All right.

‫That's pretty straightforward.

‫So let's execute that.

‫All right, so here we see select star from user over here, let's just copy paste all of this information,

‫just put it in your DB fiddle.

‫Let's not worry about that just yet.

‫And if we execute our command select star from user, what we're going to get is a bunch of information

‫because a bunch of user information was input it.

‫We can see they have an ID, they have a name, a last name, date of birth, sex on a roll.

‫Awesome, so we can see here that select star from user is actually selecting us all of the information

‫that we have around that user.

‫And if we filtered and we just said name, what we would see happen is we would only get the name back.

‫Amazing, so let's hop back into the slides and check out what a breakdown of equerry looks like.

‫So here we've expanded the query a bit because we want to break down something a little more complicated.

‫So let's say we did select name, so select the user's name from.

‫Our datasource users in the database where.

‫Rule is equal to manager, so this is new, right, where role is equal to manager.

‫This is what we call a condition.

‫So where is our key word?

‫And we're seeing where the role of the user is equal to manager return the name.

‫I hope that makes sense.

‫We're filtering data at this point.

‫We're seeing where the roll is equal to manager of the user.

‫Give us back their name.

‫And so if we were to break down this query and we looked at it line by line.

‫Select name is a clause from users, is called a clause, and where role is equal to manager is called

‫the clause.

‫These are just parts of the school statement or the query.

‫So each line here is called a clause.

‫And when we select name, name is called an identifier.

‫Now, what does an identifier and identifier is just a different word for a part of the data.

‫We know that users have a name, so when we select name, we're saying that name is the identifier that

‫we want.

‫And when we look at the last line where role is equal to manager, our filtering line, this is a bit

‫more complicated, right?

‫Where is our keyword?

‫Role is our identifier.

‫But the line role equals manager is called the condition, so a condition is something that needs to

‫be met.

‫We're saying that, OK, a user has a role, that role needs to be equal to manager in order for us

‫to get some data back.

‫Pretty straightforward and manager is called our expression.

‫We are expecting that some of the roles may be equal to manager, but some may not be.

‫So that's why we call it an expression, because we are making an assumption here that some of the roles

‫are equal to manager.

‫We want to filter based on our assumption.

‫Awesome.

‫So let's fire that real quick.

‫All right, so we have our query here ready to go, so let's run it.

‫And as you can see, we are getting back, George, Janene and Jason.

‫So let's verify that that's actually what we want.

‫So let's get back all of the information.

‫All right, so we see here, George, Janene and Jason, and we see that the role is equal to manager,

‫all right, that makes sense.

‫But who else did we have here again?

‫So let's go look at that.

‫This is a way to put a line in comment, you just you don't want to execute that line, it's a quick

‫way of turning lines on and off.

‫So let's run that.

‫So here we can see, OK, George is a manager, and then we had Maizie and Bill who are employees,

‫OK?

‫That makes sense.

‫So let's turn that line back on if we run it.

‫And we said, OK, now filter us, the employees.

‫Awesome, so we see Macy and Bill come up.

‫All right, awesome.

‫So now it's all starting to come together, right?

‫We know how to build a very, very simple query.

‫And I would push you to copy paste what's in here.

‫Put it in your DB fiddle and try to write some simple queries where you filter and you select certain

‫fields, and that way you can play around with it.

‫So we've done our break them and now we know all of the different parts that go into equerry, and that's

‫super powerful, right?

‫Because now we've just said select name from users where role is equal to manager.

‫We asked a question and we got an answer back.

‫This is what we call a declarative language.

‫School is a declarative language.

‫Now, what does that actually mean?

‫Well, let's dive a bit deeper into that.