Tutorial 12- UNIQUE AND NOT NULL CONSTRAINT Video Lecture | Postgresql: A Complete Tutorial - Database Management

hello guys welcome to our tutorial of
PostgreSQL in the last tutorial we
learned about the check constraint and
this tutorial will continue with the
normal and the unique constraint so not
till constrain is basically used to
indicate fields that cannot be empty or
cannot be null so I will be indicating
or I will be showing that with the help
of an example
so first of all I will be creating the
product stable again that we created in
the last tutorial so you could just use
it
create table products and we have a
product number that is of into your type
and it is not null so this constraint
here means that this cannot be empty
that I will show you in a while and we
have a name that is a text type it will
be not null so since we learn the check
constraint last time I could tell you
that the check constraint can be applied
with not no constraint so suppose I have
a price which I want that it should not
be null so you could just write normal
first of all and then you could write
check price should be greater than zero
so this will ensure that the price is
first of all not null and then it would
check that the price is greater than
zero so you could just execute this and
you see that the table is successfully
created so next I will be inserting
values in the table insert into products
values so suppose I enter 12 for the
product number then I insert null for
the name and then I insert minus 6 minus
5 for the price so you would see that I
have an error that is a null value in
column name that violates the check
constraint and I will enter a name that
is so so you would see that it will
again give me an error that is check
constraint is be in violation that is
negative
so this is all for the C not null and
you could see how it works
so the next thing that we're going to
learn about it is the unique constraint
unique constraint basically ensures that
each and every feed in our table is a
unique one or no value is replicated so
I for that I will be creating the table
products again so that you could
understand it better and you could
create it with me so you could just
believe this table first of all and then
I will be creating this table again the
create table for that and you could
write the product number passes of
integer type and we'll delay it as
beneath so unique a indicates that no
value can be repeated for product number
next we'll be writing that beam that is
of text type and you rise the price
America type so this was one method in
which you could declare a unique
constraint the next method I will tell
you is you could just write unique here
and declare the product number and name
so you won't need unique here so this is
the second method that you could declare
unique field in your table so now when
you would run this you could see that it
returns successfully and now I will be
entering values again first of all I
will be entering duplicate values to
show so insert into product values that
is 3
and played 100 a server installed
successfully you could see that it has
returned successfully next if I use 4
and I keep the played same you would see
I will get an error that is duplicate
key entry while its unique constraint so
see this gives me an error so this is
unique so you will write knife here and
you will see that this returns
successfully because it has changed so
tag it was in watching this tutorial in
the next tutorial we'll be talking about
primary keys so subscribe for more and
stay tuned