Tutorial 32 - Cross Join Video Lecture | Postgresql: A Complete Tutorial - Database Management

hello guys welcome to heart rescue and
in this tutorial I'm going to talk about
joins in PostgreSQL the PostgreSQL join
Clause is basically used to combine
records from two or more tables in a
database so what a join basically means
is that we are taking two tables and we
are combining two or more one or more
fields from each of the table that are
common to each other so there are five
basic types of joins in both squares QL
that is the cross join the inner join
the left outer join the right outer join
and you full outer join they're going to
talk about each and every one of them in
detail but right now we'll talk about
the cross join so the cross join what it
does it matches each and every row of
the first table with each and every row
of the second table so for example if I
see that I have two table here that
Table one is the company table so it has
around nine records and the second table
is the department table so if you see
that it has three columns now so what it
does is that it compares or it combines
each and every row of the first table
with each and every row of the second
table so for example I had nine columns
in or nine rows in my first table and I
have three rows in my second table so it
combines each and every row from the
company on the department table and if
here is the result that gives me a value
of X cross Y column in this case nine
cross three because nine is the company
table and three a third Dept table so I
get a total of 27 results when I
do a cross join across these two tables
so this could yield very large database
so actually we need to be a very careful
while using this so now I will show you
how to do cross join this is the
simplest thing that you have ever viewed
so this is only a one line command so
you could just to select the EMP
underscore ID and name and the EBT that
is the department from company and cross
join Department so this is the query in
fact would cross join both of these
tables so just execute it and you see
that we have the result and these are 27
in total
could just check it here and you see
that I have 27 results so this was all
about cross join in the next tutorial
I'm going to talk about the inner join
so thank you watching this tutorial
subscribe for more and stay tuned