 So, as I mentioned in the previous module, that in the previous module, I spoke about very very briefly the theory and the background about joins. And in this module, I will talk you and I will show you, I will walk the talk about how we use PHP to perform the join operation. And I will actually write the code, you will see the code and you will see the results and you will understand that what is the benefit of the join operation. In the prior module or in the previous module, I showed you, I told you, I explained to you that why we split the tables and then we have to join the tables. So right now in this module, we'll talk about using PHP to actually perform the join. Now before we perform the join, I will very very briefly speak about some of the useful commands which are required because when we display the results, there is a kind of a precedence or which is called as a coalition when we when the strings are used. So this is about the string processing. So let me explain it to you in more detail. So we have this over here what we call as the binary attributes and coalitions. So it means that if I retrieve results from the database. So they are sorted displayed in alphabetical ordering. If I order them, of course, if I order them. So something starting with a comes first, then something starting with B comes at the second which is followed by a and by default, if it's B or capital B, they are treated the same. Number one, number two is that if I run a query and retrieve something starting with capital B or starting with small or lower case B, it will not the engine will not differentiate. Right. To add functionality, what we do is we use the binary attribute binary attribute after the variable which we are using. So when we use this binary attribute, then the precedence is set or the coalition is set. Right. And there's a difference between small b and capital B is a difference between banana starting with small b and difference between banana starting with capital B. That is one thing. The other thing is the unique constraint. The unique constraint what it does, it is similar to the primary key which creates an index and there is no repetition on the column within the column for which the primary key is applied. The same is true for the unique constraint, but there are differences also unique constraint is slightly different. There are two differences of unique constraint as compared to primary key. That I will go into the detail when we go towards the detail of this particular module about this running and performing the joints using PHP. And then is the enum data type. This is enumeration. So what it is saying is that in this column which is text column, we can only have certain strings. For example, in the gender column, we can only have male or female. And for the same, for example, it is the type of movie. We can only have the fiction or we can only have comedy and so on. So that is the end. So this is the type which we assign to the columns and use these commands to ensure those columns are there. Okay. Then of course, when we retrieve the data from the database using the SQL commands, we can reduce the number of rows, we can order them, we can group them, we can sort them, we can summarize them, we can do all sorts of those things. Right. And remember that these things are not happening on your client end. On client end, you make the request that request is passed through the second tier, which is the your application tier and then go to the database tier. And from there, the results are sent to the web server and the pages are generated. So this is more which I will be covering. And this this part very interesting part, which we will cover in the detail part where we create the forms for this fictitious book store, which I'll be talking about. So right now I'll be talking about some details about pulling data from multiple tables. So let's look at some examples and let's look at some code over here. So over here, let's look, this is the command over here, this is the MySQL prompt over here. And I would like to know that how many pages, okay, what were the URLs for which the pages were accessed. So I get only number four, that is fine. But what is not fine is, is I really don't know which people accessed with which pages. So I change the code. So instead of from this message log, I also look at the member ID, okay, and from the access log. So I just access log also. And now I am counting the page URL. So what I get, this is the member ID, okay, this is the member ID over here, one, three and six. And we see that this member has access to pages. Now that is useful information. But that is not very interesting information. Why? Because it is very difficult to connect the member ID with the member itself, especially when I have tens of thousands of members, right? So this query over here, this lists all the first names and the last names of my members. So for the sake of simplicity and the size of the screen, we are only showing results from a very small database. You can see that we have these members, okay, and we have the six or seven members over here. And now we know that member one is John, okay, and we know that member three is, and so on, who is member six and so on. So these are all the members. Now, up till now we have not applied the join over here. Up till now, up till now we have not applied the join over here. So what I'll do is now I will apply the join. You can see the results. So this is the join. This is the join over here. This is the join over here, okay, so I have now used the join. And based upon this join, now I have the link between the member ID and the member name. So now I have very useful information. So you see in this module, what we did was that I showed you very briefly that what we are looking at and then the limitations of what we are getting. And then we apply the join and get the results. And if you recall, in the first module of the course, I spoke about, I talked about, I gave you the idea that we are going to use a hands on approach. We are going to open the hood and fix the problem over there. And we are going to have an understanding. So this is the step by step approach of the understanding, which will be following in this course. And of course, you are welcome to ask questions. And we will be very happy to answer your questions.