How to join
4 Tables In Postgresql
PostgreSQL: Inner Joins | Course | 2019
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all right now that we have a foreign key
constraint between our two tables person
and car let's go ahead and learn about
in their joints so any joints is an
effective way of actually combining two
tables and the way it works is that you
have a table a as well as a table B and
what you want to do is actually combine
these two tables now the inner join
takes whatever is common in both tables
so if you have a record inside of the
table a and also a record inside of the
table B so if you have a foreign key
which is present in both tables then it
takes those two records and then gives
you the result of both which we're going
to call it C so a plus B equals to C and
to recap an image Oien takes two tables
and B and then if we have a foreign key
that is present in both tables then we
have a new record called C let's go
ahead and learn how to use any joints
with Postgres all right now that you
know what a join is let's go ahead in
this video perform a join between our
two tables car and person so I'm gonna
select star from person and also select
and then start from an in car so we want
to perform a join based on this foreign
key right here so car ID links to this
ID inside of this car table so to
perform a join we simply have to say
select and then star so we want to
select every single column and then from
and then here is where you specify the
first table so person and then don't
press semi column and then on a new line
simply say join so this is how you join
to another table now you specify the
actual table that you want to join in
our cases car
and then you need to say on so on takes
a column which can be used to join these
two tables so in our example is the
foreign key so car ID found in person
will join to ID found in car so let's go
ahead and say person dot and then car
underscore ID equals two and then car
dot and then ID if you go ahead and
press semicolon press ENTER you can see
that we've got two results and in fact
because you can't see properly I'm gonna
show you a nice trick so if you press Q
and then press backslash and then X and
then enter you can see that we have
expanded display on now if I perform the
same Select you can see that now we have
this information that can be easily read
and there we go you can see that would
performed a joint between two tables and
pretty much this right here is Oh
actually sorry this entire selection is
everything from person and then the rest
is from car and you can see the same for
Fernanda so Fernanda right here she has
the car ID of two and you can see that
this is the actual car and this is how
you perform joints so obviously so if I
scroll up so obviously Adriana is not
included because she doesn't have a car
so remember a joint simply links to
tables where the primary key and the
foreign key is found in both tables so
just let me go ahead and show you one
more thing so you saw that we selected
everything so select star from person so
what we can do just I mean remove that
so so you can see that we get every
single column so now what we can do is
just grab certain columns from each
table so to do that let's go ahead and
say sell leg
and now I can go ahead and say person
don't
and then first name and then comma let's
go ahead and select the car don't and
then make comma car dot and then model
and then car dot and then price and then
we can go ahead on a new line so if I
play the screen on a new line from and
then person and then we going to join so
let's join and then car on and then
person dot car underscore ID equals to
car dot ID semicolon if I press ENTER
you can see that now we selected only
the columns that we wanted and let me go
ahead and remove this expanded display
on and to turn it off back slash eggs
it's a toggle now if I perform the same
selection you can see that if I remove
that you can see that now we simply
selected few columns from each table and
this is how you perform a join in the
next video I'm going to show you how to
perform a left join join me there see ya
![Joining Multiple Data in PostgreSQL [UR] Module 4 Lecture 3 ZE - 270](https://img.youtube.com/vi/pL9AxJhYEcU/mqdefault.jpg)