join

SQL Tutorial - 29: SQL JOINS



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hello guys welcome to my channel this is

the 29th tutorial in this course and in

this tutorial we are going to talk about

SQL joints now those of you who heard

things about joins like you know joins

are really difficult and you know it's

impossible to master joins and all those

things you know I guess you would have

to put all those things at the back of

your mind for this tutorial because

joins are extremely simple but very

powerful and you know at some point of

time in your life if you want to make a

career as a database administrator then

you would have to learn joins and also

use them extensively right now work for

an MNC of five months as a database

administrator and all I did everyday was

just used as to a joint and pull out

stuff from tables right so the reason

why SQL joins are popular and so

powerful is that joins allow you to pull

information out from more than one table

right so for the sake of this tutorial I

have created another table and I've

given that table the name tutorial

underscore info so we've seen the

tutorial table in you know the previous

tutorials and let me show you guys the

data that I have in that table so for

that I'll use the Select query type in

select space star since I want to see

data in all rows and from and then the

name of the table which is tutorial put

in a semicolon at the end when I press

control enter I see that this table has

got ID field and title field subject

field duration and applaudin scored date

so in ID I have got a unique number for

all the rows in the table and the title

field holds the title of the tutorials

and subject field holds the names of the

playlist so I've got SQL C in shell

scripting and then duration holds the

length of the tutorials in minutes and

then uploading score date field holds

the date on which the dear old was

uploaded right so this is the tutorial

table and I have created another table

in this ones tutorial underscore info

and this holds information about you

know the number of views for each oil

the number of likes each oil has and

dislikes and shares and you can see that

I have a column in this table which is

tutorial underscore

or ID and it holds a similar information

as the ID column held for d2 role table

right so it also has a unique number for

each row and well this row actually

corresponds to you know the first row of

the tutorial table right so all this

data that you see you know 15,000 views

and 54 likes and 13 dislikes and 6

shares this data is for the first

tutorial or the tutorial with ID 1 in

the tutorial table now let's say you

want to see all this information as well

as some information from the tutorial

table in a single result set and you

want to pull all that information out

you know through a single SQL query well

how are you going to do that because

till now all these select queries that

we've seen in this course all those

queries have just pulled out information

from one table but here we want to see

you know views likes and shares from

this table and we want to see title

duration and subject maybe from the

tutorial table so you know if you want

to do such things and you have to use

SQL joins and the way you're going to do

that is you'll have to use the Select

query of course and you will first type

in the columns that you want so let's

say I'm going to refer to the tutorial

table as T right and we're just going to

use aliasing and if you don't know what

that is then I would suggest you to

watch the previous tutorial in this

course in which we talked about the ask

laws but I'll just type in T dot and

then the name of the column that I want

from the tutorial table so I want ID

from the Detroit table and then I want a

let's say title and I also want duration

okay and then on the next line I'll type

in the columns that I want from the

tutorial underscore info table and I'm

going to refer to the tutorial

underscore info table as Ti so I'll type

in t I dot view and then T I dot likes

and then T I dot shears and I guess

that's that's good enough and then I'll

type in from on the next line and then

I'll type in

tutorial right and since I have referred

to the table tutorial as T in the kawaii

thus far I'll have to instruct test

whether I have done that and for that I

will use the as clause I'll type in T

here and then on the next line I'll type

in the keyword join right and this is

going to instruct SQL that well all this

you know information that we are looking

for this is not present in just the

tutorial table but let's present another

table and the name of that table is

tutorial underscore info and since I've

referred to this table as Ti I will type

in a space t I here and then on the next

line I will type in another keyword and

this one is on and what this keyword is

going to do is it's going to tell SQL

that you know this joint operation has

to be performed on some condition and

that condition is that we want you know

data from both the tables for those rows

for which the value in the ID column in

the tutorial table is the same as the

value in the tutorial underscore ID

column of the tutorial underscore info

table right so it may sound complicated

but if you just think about it then it

will all make a lot of sense so the way

I'm going to write this condition is

I'll type in T dot ID and you know it

should equal the i dot tutorial

underscore ID right I'll put a semicolon

at the end and when I press control

enter I see that I get a result set in

which all this information is present

right so I have the ID column and then

title duration views likes and shares

and now I can see the number of views

for the Select query tutorial number of

likes for a number of likes for the

insert query table without having to

execute the Select query for both tables

separately right so this is about SQL

joins and there's another way in which

you can perform the join operation and

that's actually the more used way and

also the less preferred way and you know

this is this is the right method

actually and you know this is the method

that you would see you know professors

teaching in universities and you know

the method discussed in textbooks but

the more used way of performing SQL

joins is you you remove the join keyword

from your query you just have your table

name so tutorial as T then you put a

comma and then you type in the second

table name tutorial underscore info as

Ti and then on the next line on the next

line you type in where right so you type

in the where clause and then the

condition so that would be T dot ID

equals t i dot tutorial underscore ID

I'll put a semicolon and when I execute

the query I see that I get the same

results that there's nothing different

in this and you might think that this

query is the same as the previous query

but actually they're very different but

you know you can you can actually learn

through anyway but it would be great if

you you know practice the previous query

more and you master that more because

you know that is the recommended way of

performing the join operation right so

thank you so much for watching this

tutorial and you may subscribe to my

channel and I'll see you soon