SQL Tutorial - 8: Constraints in SQL Video Lecture | Microsoft SQL for Beginners - Database Management

hello guys what my channel this is the
eighth tutorial in this course and in
this tutorial we are going to talk about
constraints so we're going to understand
what a constraint is and the several
options that we have available with SQL
so these are the constraints that we
will be discussing in this course so we
will be talking about the not null
constraint and the default constraint
you need primary key foreign key in
check so we're going to talk about the
first four in this tutorial in the last
two constraints the foreign key and the
check constant we're going to talk about
later on in the course when we discuss
some fancy things such as joins and
stuff right so let's start with the not
null constraint so if you're creating a
table in which there's going to be a
field that you want to have a value you
know for each and every row that's there
in the table then you would want to use
a not null constraint with that
particular field while creating the
table so what I mean is if you've got a
table that's going to have three fields
let's say name and ID and email address
and if you would want the ID field to
have a value for each and every name in
the table then or each and every row in
the table then you would want to use a
not null constraint for it because if
while populating the table using the
insert statement in SQL you would the
you know miss giving the value for the
ID field for any row then you would get
an error message and the insert
statement won't be processed right so
that's the utility of the not null
constraint and we'd be checking it out
the syntax of it and everything while
you know discussing the create table
statement the next constraint that we
will be talking about is the default
constraint and as the definition says if
while populating a table you miss giving
a column some value the default value
will be used so when we talk about the
create table statement we'll see that
you know with the create table statement
you get an option of specifying the
default value for a particular field and
that's pretty handy because if you're
creating a table in which a field is
going to get the same value for let's
say 90 percent of the records then it
makes sense to you know specify that
value in the create table statement
itself because that's going to say
load of time and you know while
inserting data in the table or while
populating it you don't have to specify
the default value for that field you
know for each and every entry the next
constraint is the unique constraint and
the unique constraint makes sure that
all values entered for the field on
which the constraint is applied are
different so it makes sense I'm sure
that you know if you want something to
be unique then you have to specify to
SQL that you know you want that field to
have a unique value so what happens in
case you applied the unique constant on
a field and you try giving a duplicate
values well so obvious you get error
messages and you know the data that you
you know enter for a field once you
cannot enter the same data again if
unique constant is applied on it if you
try to do that the insert statement
won't be processed and you know you just
get error messages and the last
constraint that we're going to talk
about in this tutorial is the primary
key constraint and this is perhaps the
most important constraint the available
to us in SQL and it's a combination of
not null and unique so the primary key
constraint makes sure that you specify
some value while populating the table
for the field on which the constant is
applied and it also makes sure that the
value that you've entered is different
from all the other values that exist for
that field you know in the table before
you enter the latest value so as the
definition says some value would have to
be provided in each row and all the
values entered must be different so
we're going to see all these constraints
in action later on in the course when we
you know check out the create table
statement we're going to discuss the
syntax and then also while discussing
the insert statement we see you know how
if we try to violate these constraints
you know SQL throws error messages at us
and we are unable to you know populate
tables so I hope you had fun watching
this tutorial and please subscribe to my
channel in case you have already I'm
going to see you in the next one and
thank you