WEBVTT

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I will call you back again to another video lecture in MySQL.

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And in this video lecture we go ahead and look at the primary keys.

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Alright.

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So the primary keys are very important because it helps us to be able to manage our database very well

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without mixing up things.

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It helps each data to be able to have a unique value.

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So if you have a IDs especially, this is where you.

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I will advise you to always use the primary keys on your IDs so that you can actually differentiate

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your data.

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So you can have different IDs, have maybe some first name, the same last name with different IDs.

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Let's go ahead and do something very interesting here.

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I'm going to create a new table and I'm going to use that to explain everything.

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Then you go ahead and apply that to the employees table Stable and the student table.

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Now I'll go ahead and create a table and I'm going to call that table.

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I'm going to say table.

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And the name of the table is going to be teachers table.

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Alright.

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So I'm going to list all the teachers in the school because we have our school database.

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Now all teachers in school, I want to put them together and in order what I'm going to create this

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teachers I might have teachers that have the same first name or the same last name.

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I can still have teachers that have the same first name and last name.

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Yes, it's very possible.

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So I can say the first one is going to be teachers ID or teacher ID that is okay and it's going to be

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an integer.

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All right.

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Now it's going to be an integer because they're going to take like 1234, five, 678 and cool.

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And now the next one is going to be the first name I would say the first underscore name.

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All right.

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So I'm going to stop in the first name.

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And this is going to be cha.

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And it's going to be three characters.

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So you can go ahead and add a last name salaries and so on.

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Or for the quality purpose.

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And for the purpose of this, I just want to stop at this so it can be easier for us to actually understand

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what's going on.

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So I can add a permanent key to the first name.

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Maybe I know what every teacher to have the same first name, which is not possible.

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You understand that is not possible, that teachers will not have the same first name, because two

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S's might answer the same thing or the same name.

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So let's go ahead and put the primary key to be under the teacher's ID, meaning that I'm going to have

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these different numbers.

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So I'm going ahead and saying the primary go ahead and make this to be uppercase.

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So the primary key.

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So if I add this primary key it means that even a null value cannot be added.

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De.

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Yes.

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It does not accept a no value.

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Okay.

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Now let's go ahead and uh select.

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Oh let's go ahead and select all from.

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Teacher.

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Okay.

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Select all from teachers.

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And go ahead and press semicolon at the end.

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Now let's go ahead and execute this query.

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And we have the table.

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Teacher ID first name.

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And uh at the moment nothing is in there.

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So now I have this teacher ID and I set the teacher ID to be null.

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And let's say you have this assistant table because most of us will be like, okay, should I go ahead

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and create a new database of employees or students?

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No.

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If you have a table already, just go ahead and do what I'm going to do right here.

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I'll go ahead and remove everything here.

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So go ahead and delete this.

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And I'll go ahead and say alter your table and you select the table name maybe the employees or the

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student table.

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Which one of them Go ahead and say maybe it'll go ahead on the table.

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And if I refresh this, I'll have to start over in here.

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So if I go ahead and set adjustable I'll go ahead and, uh, add the constraint and then the constraint

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which is the primary key.

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Then you specify where you want the constraint to be applied and say it's going to be under teacher

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underscore ID.

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And then plus one at the end of that if we go ahead and run this we're going to get an error because

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you have already um set the primary key for that.

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So go ahead and run this.

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Let's check it out.

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And down here you can see I have multiple primary key defined because I have already defined the primary

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key.

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The first time I created this table.

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So I'm just showing you this in case if you have a table you want to add a primary key to, just go

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ahead and add constraint primary key.

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Then select the column you want to add this primary key to.

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Do you understand.

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Now let's go ahead and attempt to add some things under here.

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So if I go ahead and run this code, I can still see my teachers ID first name right in here.

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Now I'll go ahead and set some things inside here.

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Let me go ahead and say go ahead and insert into.

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Insert into teachers and our ahead and insert values.

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Then the value.

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Go ahead.

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Semicolon at the end.

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Then I'm going to add the workforce parameter 1 or 1 for the first ID.

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And I'll let the name be equal to.

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George.

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All right.

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Now let's go ahead and execute this query.

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And I have 101 George and I consider the first name is George and the ID is 101.

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All right.

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Now let's go ahead and change this to like our 102.

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And then we change the name to like Steve.

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And go ahead and execute cutest query and have One02 and Steve and you can see that.

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Now I want to have the same name.

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All right, let's go ahead and give the same name.

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I say go ahead and say 103.

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And uh, the judge again then is a 3D query.

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You can see I have George the first time, first name and second name George.

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What I have different IDs.

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And that is really very interesting.

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What if I should go ahead and attempt to add A10?

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Let me say 101, but different name.

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Steve.

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Steve is already a.

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And let's go ahead and execute this.

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Or let's go ahead and give it a different mentality.

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I'm going to say memoir.

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And I have to add 0101.

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Go ahead and execute this.

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And now I'll drag this up so you can be able to see an error message.

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It says Duplicates key.

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1014 teacher for teachers table.

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That is the primary key.

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So 101 for key teachers does primary.

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That is you are not authorized because it's already duplicate.

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Okay.

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So we have A101 and we have another 101.

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So it is already duplicated.

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Now what if I say okay now I have known that we have duplicates.

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And what if I change that to be null.

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While I change this to be null.

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And I'm going to call this maybe a Steve.

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And if I run this, then now again, because you have an error, it says teacher ID cannot be null.

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So teacher ID cannot be no.

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So you can either go ahead and change that to 104 and go ahead and click on that.

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And you can see we have done here.

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101102.

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Steve 103.

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George 104.

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Steve.

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So they can have the same first name, the same last name, and so on.

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But the ID need to be different.

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Okay.

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That is very important.

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Now let's go ahead and find the child with an ID 103.

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So go ahead and delete this.

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And I'm go ahead and say.

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Teach us ID.

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So select ID from teachers.

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Then we're going to set this guy.

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Let's say we.

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Teach us okay.

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We're the first name.

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So select teachers ID from teachers where the first name is going to be equal to George.

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So listen, we can at the end of this.

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Now let's go ahead and run this and check it out.

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So go ahead and open this.

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So this is teachers ID.

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You see teachers ID first one is 101 and 103.

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So if we change that to teachers ID where it is Steve let's go ahead and run this again and check it

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out.

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Let's go ahead and open up this.

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And that is 102 and 104.

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All right.

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Cool.

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So what it is you can see select a from first name via teachers ID or we have teacher ID is equal to

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101.

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All right.

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So go ahead and run this and check it out.

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Open up this.

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And that is George.

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So if we check now if I were to select individually two.

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And the guy hadn't executed.

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This guy hadn't opened it up.

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And you see first name Steve.

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So in that way, you can actually use the IDs separately to check all this.

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And anyone I check to open up this, that is one zero is also George.

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So in that way you can be able to use a primary key and work with anything you ever want to work with.

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And it will help you to make sure that no two teachers have the same ID, and no teacher has a no value

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in their teacher ID, so the probability is very important in your database design and ensure you master

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that play around with it.

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And if you have any questions, go ahead and use the question and answer section.

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And I'm going to get back to you as soon as possible.

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Thank you so much.

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And I'm going to see you in the next video lecture.