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[Music]
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hello friends welcome back to our channel so in today's session we'll discuss about the common constraints
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which we are being used in the sql while creating the table so constants our topic is
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constraints so what are these constraints right so generally these constraints are
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given for the attributes while creating a table right so constraints are nothing but some rules
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rules while creating a table we have to give some rules for the attributes okay while inserting the data
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while accepting the data so what are those constraints the the common constraints the common
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constraints so let us discuss about the primary key what is the primary key
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not null
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check default
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unique
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foreign so these are the common constraints we are going to use
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uh while creating a table so previously we have seen the command for creating a table and we have seen the command for
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inserting the values into a table but there we have not given any constraint for the
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attributes but here we can give the constraint so let me explain you about the theoretical part that means what is
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this constraint if you give this constraint for that what happens i'll explain here and after this we'll move
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on to the sql command line and i will execute each and every uh constraint okay i will demonstrate each and every
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constraint by writing the query that means we will create a table with each and every constraint i will explain everything okay so first one is a
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primary key if if we have given an a primary key attribute i mean any
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attribute as a primary key it will be having the two characteristics one is by default not
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null that means the user should not leave it as a blank so while inserting the data if the user
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left the blank that means if user doesn't give any value for that particular attribute so by default the
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attribute value will be null so there is a one more constraint not null if you give this not null it should
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not be accepted okay it should not be left blank so compulsory the value should be given
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by the user while inserting the data so here if you give the constraint as a primary key for
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any attribute so by default the not null will be applied
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and also
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no duplicates so duplicates were also not not allowed okay if it is a primary key if any
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attribute is given as a primary key duplicate should not be allowed so let me explain here so create
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table student
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okay so we can give a multiple multiple line we can write the query in a multiple line unless you give the
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semicolon because the semicolon is a termination of the query so here i'll write some s id
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some integer comma some s name
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somewhere cap which is of a character data type of some 30
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okay and a branch of a wear cap
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of 20 percentage as a float
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and here you need to write the primary key that means a constraint after declaring all the attributes then we can
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write the constraint a primary key so which one we want to give which attribute we need to give the primary
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key in a parenthesis so s id so this will create a table student with
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the four attributes s id name branch and percentage and this s id will be treated
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as a primary key which should not be kept null and which should not accept the duplicates
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so i'll execute this query and i will show you okay so after creating a table i will execute that one and also i will
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try to insert the values with the duplicates as well as with the null values i will show everything okay all
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the cases will see so this is how we can give the constraint primary key and coming to the
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not null so if you specify any attribute with a normal constraint that implies so
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it should not be kept blank so while inserting the data we have to give a value for that particular attribute and
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while creating a table here so for which attribute we want to give a not null that should be given
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after the after declaring the variable so here s id integer same branch where can percentage float here i give a not
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null here i'll give a not null so if i give a
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not null that implies this normal constraint is given for the percentage so percentage should not be kept kept
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blank for all the students any student okay we have to give a value for the percentage for the student it should not
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be null it should not be the default value is not null okay we have to pass
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the value we have to pass the value we have to give the value we have to insert the value right so that is the normal constraint
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and check the name itself indicates check means before it taking the data
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from the insert command before inserting the data from the insert command it will check the condition which we are giving
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and if the condition is true then only it will be accepted the data will be accepted into the table for example let
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us take one more uh attribute that is the age
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age which is of a integer okay after that we ready to write the conditions so constraints sorry not
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condition constraints so i write the constraint a primary key which is of sid
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and then we can use a check constraint check age
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greater than 18 so if i execute this one so it will
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create a table with attributes student id student name
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branch percentage age all the five attributes will be created
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okay and in that the primary key is set for the sid and
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not null is set for the percentage and check age greater than 18. so while inserting the data
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if you give the value for the age which is less than 18 it will not be accepted
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okay while inserting the data so we have to insert the age value which is a greater
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than 18 then only it will be accepted and that that that data only will be inserted into the table if the age is
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less than 18 the data will not be inserted into the table that means before insertion it will check this
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condition okay so this is also will execute the query and i will explain everything
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so that is a check and the next one is a default default so we can give we can set the
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default value okay we can set the default value so let us take the
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i will remove the branch okay i will take the college
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college where can of 20
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and here i can set the default college okay so
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here only we can write a default quotations let us write some college name here
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right while declaring the attribute itself we can write the default value so default value will be this one and
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unless i mean if you are not giving any value for the college by default it will be taken as a bc
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if you are giving any value for the college that value will be taken as a consideration that will be i mean this
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bac will be replaced with the given value okay while insertion we have to pass all
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the values or we can give i mean required values okay if you want
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to insert a required values required attribute values for the required attributes so we need to give specify
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the attribute names in such case if you are not giving any value for the college
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by default it will be considered as this default value okay whatever the value we are giving as a default that will be
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taken right so if you give any value for the college this default value will be replaced with
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the given value right so i will explain you i will demonstrate by executing the query right
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and the next one is uni which is similar to our primary key which is similar to our primary key so the same thing
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same thing okay but the only difference is it can accept the null value but it
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doesn't accept the duplicates it doesn't accept the duplicates but it can accept the null value right for example we have
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seen the unit unique as a contact okay or email so it is not mandatory that every
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student should have the contact number or every student can have the email so if we can left blank okay we can left
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blank or you can simply yes we can left blank right so such cases we can give the unit so
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here instead of giving the age okay
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here itself i'll give a contact
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as a integer followed by the constant unit and
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the default that is the primary key of yes id
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so automatically the contact number will be unit that means if you give the same
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contact number for two students it will not be accepted because it doesn't accept the duplicates it doesn't accept
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the duplicates but you can left blank here okay that's the main difference between
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the unit key and the primary key so primary key doesn't accept the null values unique can accept the null values
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but it doesn't support the duplicates similarly primary key is also doesn't support the duplicates so that is a
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unique constraint so for this also we'll execute the query and coming to the foreign key
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we have discussed about this foreign key the mainly foreign key is used to relate to different tables okay
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relate to different tables for example
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so i am having a two tables student
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student with a s id yes name and a core sign
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course id and there is a one more table called course so which is of c id course id and course
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name and you know that course id is a primary key yes id is a primary key okay and
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course id in the student will be the foreign key so this is a primary key
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this is a primary key and one the primary key of one table will be the foreign key of another table
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so this will relate the two tables this will relate the two tables so for
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this one let us create table
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course c id integer
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c nade where of
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30 and
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primary key of ci so there will be some space time
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primary key this is some space so
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right primary key and this will create a course id and then
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while creating the primary element while creating the student id so create
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table student so how many fields we have to create three fields so s id with the integer
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yes name as a where can of some 30
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and then cid as an integer
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primary key what's the primary key for the student
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table sid so s id and we have to give the foreign foreign key so here we we
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have to write foreign key of
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cib foreign key of cid which references the primary key of course
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ca so here you need to write references
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course of c id course of cl so
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the course of cid that will see course id will be the primary key of course table which references the foreign key
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in this student table so this is the syntax to create the foreign key
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by creating a table right so this is how we will
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create a foreign key for two different tables and so i am not i i will execute
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the same thing in the sql so i will show you the queries i will show you that i will demonstrate each and every
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constraint so how the primary key can be set as a constraint and how the not null
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check default unique in the foreign key i will execute each and every query in the sql so let's move on to the sql
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prompt hello friends so just now we have seen the syntax for
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the common constraints which can be applied while creating a table in mysql
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now let us see the implementation part of each and every constraint so first let me open the command line
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mysql so i will give the password
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so just clear the screen now let us enter into the database so let us
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check the databases which are available in this mysql so we have created one database
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that is a youtube so let's let us insert i mean enter into that particular database so use
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youtube sorry use
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youtube now we are in the youtube now let us check what are the tables available here
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so we have created a student table with four fields like student id student name
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branch and percentage so we have not given any type of constraints here okay so
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we'll delete this table and we'll create a one more table the same student table
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with the same fields but by giving the constraints so let us write down the constraints first
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let me write down the constraint first so the first one is not null
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so if you give this constraint for any attribute so the null value will not be
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accepted that means the user have to give the value for that particular attribute so the user need is not i mean
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is not able to leave that attribute blank and the next one
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is the primary key primary key means
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it will avoid the redundancy so the duplicates will not be allowed and by default
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it should not be kept as not null okay by default it should not be kept as enough
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and then check so while giving the value we can check some
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condition and if the condition is true then only the value will be accepted so that will
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discuss uh by executing the query right so then default so we can set some
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default value so if the user doesn't give the value for that particular attribute this particular
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default value will be taken and then unique
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unit so this is also similar to our primary key but only one difference is it will avoid the redundancy similar to
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our primary key but the difference is it can have the null okay the the value
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of this particular attribute which we which we have given as a unit can accept the null value so primary key it doesn't
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accept the null value and then foreign foreign key that means to relate
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one table with another table okay so these are the common constraints we have
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seen just now so now we will create a table by following each and every constraint so let us check with the each
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and every constraint now so first let us check with the primary key let us check with the primary key okay
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so let us drop this one so drop table student so that the student table will
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be dropped so now you can observe show tables so it will return empty set because the complete student table has
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been removed from the youtube database right now
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let us create a table okay so we know the syntax for creation create
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table table name and give the attributes
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so give the attributes the first one is a student id which will be of a
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number okay
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then let us take an integer by default
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next second parameter s name okay student name which is of a
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varcat of some 30 characters it will accept next
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branch which is of a wear cap again it will accept some 20 characters
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percentage which is of a float value right after that we have to give the
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constraints now i will give the constraint primary key primary key of
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here we need to give the primary key which is which we have to give the primary key so i will give sid as a
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primary key that implies if you give the same sid for the two student details it will not be accepted
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and if you left this sid while inserting inserting the values it will not be accepted because
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the characteristics of the primary key is by default it should be not null and also it should not be
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repeated so just we are giving the primary key now okay
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so query okay zero rows affected that means we have created a table now you can see show tables so there is a
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student table you can observe describe student will give the structure of a student table see
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student id integer no null is no so that means null is i mean we can't left this s id because of
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a primary key because of a primary key okay now
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we'll insert some values and we'll check so insert
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into table name values and here we need to give all the details
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okay otherwise if you want to give some particular attributes not all the four
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you have to mention the attribute names so here i am giving all the values so 1 0 1
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and s name sandeep and branch
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cac and percentage 98
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right see one row affected you can sell you can check with the student database
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see one row is there now insert into student
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values again i'll give one of one one not one
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some other name sarathi cse
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95 so we should get an error because here the s id is a primary key it should
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not accept the redundancy that means the duplicate values here the first row the student id
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is 101 and the second row we are just inserting the second row and we are giving the same
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101 as a student id so if you execute duplicate entry 101
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for key student dot primary that means the primary key we are given we are we have given sid as a primary key so it
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should not accept the duplicate values for that particular attribute okay it should have only the unique
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values so while insertion itself we are getting an error otherwise
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so let us insert into student and
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give the attribute names like s id s name
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branch values so one zero two samsara
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and the branch is some easy execute see query okay one row affected
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so we have given only the three attributes so in the previous class we have seen the syntax for the insert command so
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there you can insert all the values or only a few attributes values for a few
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attributes if you want to give values for few attributes that attributes name should be mentioned here so here i have
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mentioned only three attributes and i am giving only the three values so we have skipped the attribute percentage so by
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default it will be null let us say so select star from
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student see by default it will be null now again
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i will execute the same thing but here now i just want to
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skip the s id okay so i just want to skip the sid s name
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branch and i'll give the percentage percentage so i'll give
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take the so first i'll give the branch name branch and percentage let it
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be 99 execute see field sid doesn't have a default value
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it doesn't have the default value you can observe here so not no null no null
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so it should not be kept null okay it should not be kept null
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because sid is declared as a primary key so primary key
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characteristics are one is redundancy it should not accept the duplicate value second one is it should not be kept null
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so for every row there should be s id okay not null not now
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right so hope you understood the constraint primary key constraint primary key
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i'll change the order here right primary key so accept the primary key we
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can give a null for all the things see once again insert
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i will tell you so i i'll just insert the sid okay i am not giving any value for all
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the remaining attributes so one zero three execute you can observe carry query okay
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one row affected and you can see select the star from student so that
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the third one is 103 and all the remaining values kept null because we didn't give any constraint for these
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particular attributes see sid integer where care
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worker percentage and primary key we have not given any constraint as in not terminal not null so it will accept a
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null value right so this is the primary key now let us drop the table
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and we will check with the not null okay not null so
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drop table student so actually we need not drop the table we can use the alter
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command to give the constraints but there will be a little bit confusion so i'll first let me explain you about all
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the constraints and then we'll see the alter commands okay so we can add the constraints by using the alter
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so that we'll discuss in the next one right for better understanding and and just to drop i i'm deleting the table
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and i'm i'm creating a table with multiple constraints so drop to build table student so it was dropped now you
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can observe show tables so there will be no tables empty set now again we'll create a table
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create table student
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so first one sid which is of integer yes name which is of a wear cap of a 30
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maximum and branch okay
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branch and where care
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of a 20 percentage which is of a
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float and i i just want to give the percentage i don't want to keep a null value for this percentage so
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give the constraint here itself so not null that implies this percentage value
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should be given by the user so it should not be make blank while
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inserting the values so i will give the primary key primary key will be the s id
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right so you can observe so we have we are creating the table
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student with a sid integer s name where care branch worker percentage float and we are giving a
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primary key as sid so it will be not kept blank and percentage i am giving one more constraint not null for the
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attribute percentage so the user how to give the percentage
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okay how to give the percentage the user is not able to left blank for this percentage while inserting the values so
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we'll check so now you can observe query ok zero rows affected so
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if you apply the show tables it will display the student you can see describe student
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see float null value no null it should not
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keep blank okay and we can leave the s name and branch but we should not leave
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the sidn percentage let us check so insert into
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student okay values let us take 101
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sandeep cse
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and 98
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so query okay okay now select star from
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student you can get a complete details now let us check insert
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into student give the names sid
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s name values 102 and s name sarath
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so it will not be accepted because the field percentage doesn't have a default value so you can observe here so we are
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giving a constraint not null for a percentage that implies the user have to
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give a value it should not be kept blank for example if you modify the same query
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so we are giving only the s id as well as percentage
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so it will be accepted because the remaining two that means the name and branch we are not giving any
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constraints so it can be left blank so 97 see query okay
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select start from student you can see a null will be given for s name and branch because we are not
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giving any constraint for s name any branch we are giving constraint for percentage as a normal and primary key
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as a sid so these two fields should not be kept blank we have to pass the value we
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have to give the value for these two fields because of the constraints
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right so hope you understood this not null not null and the next one check so before
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inserting the value we can check the value and if the condition is okay then
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we can add the value so let us check drop a table student and just deleting the table you
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can see show tables there were no tables empty set so i'll create a table student
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with the different attributes sid with the integer yes name with the wear care
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of a 30 branch as a wear cap
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of 20 age integer
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okay percentage or leave the percentage let us stop here so
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primary key of sid
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and then check age greater than
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18 check age greater than 18 and uh so if you are passing the
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value for h the if the age is less than 17 the row will not be the value will not be
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accepted that means the row will not be inserted so let us check
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create a table student side
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integer s name where care of
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20 characters branch of where care of
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30 characters age of integer
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primary sorry primary key offer sid
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check age greater than 18
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right so now we have given this particular
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check constraint so while inserting the data into this particular student details
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if the age is less than 18 if the user gives the value of age as less than 18
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the data will not be get inserted into the table let us check see describe
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student so it will give the complete structure of the student now let us check insert
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into student values so one zero one
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sandeep what's the next one branch so csc you know what's the age so let it be 20.
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so one row if i affect it so let us check the details select star from
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student so we'll get the details now we'll try to insert the data
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okay so whose age is less than 18 so 102
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so let us take some saradi and easy
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and i'll give some 16. you can check so the data will not be get inserted
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into the table because we have given this check constraint and we are checking whether age is greater than 18
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or not so if the condition is false automatically the data will not be get inserted so you can
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observe here here we are giving the age of 16 so we got an error check a constraint student check is violated
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so if you update this value as 19 it will be accepted
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so you can select you can see select star from student you'll get the details
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so like that we can also give the constraint check we can give the constraint
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check okay so we have to give the some condition based upon that condition
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if the condition is true then only the value will be inserted into the table
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let us check constraint now default construct so i will drop the table once again drop
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table student so system
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cls so here the default constraint means we need not pass if the user doesn't
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doesn't give the value to the attribute the default value will be taken as a consideration so we can set the default
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value okay we can set the default value for any attribute so let us create a table
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now so now we'll create the table by giving
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the default constraint so create table student
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and take the sid as an integer and s name as a where care of 30. and
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branch with a wear care of 20 and let us take one more
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field that is a college which is also a wear cap of 20 and let us set the default so
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default give the college name i'll give the college name as a bec so if if the value
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is not given by the user to the college field so by default the college will be the bec
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so let us set the primary key as s id
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you can check the query is ok so 0 rows affected so let us check select solve
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show tables so student so describe student so it
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will give the structure of a student see the default value is a be easy okay now let us insert the data so
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insert into student values
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values so here we need to pass all the values here okay you here you
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are not specifying the attribute so we need to pass the values for all the fields so let us take one zero one
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sandeep cse and college some gec
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so one row is affected okay one row is affected that means we we have to pass the value here
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and if see select star from student one row is
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inserted now let us take insert into student
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right here if you want to pass sid s name and
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branch i am not giving any value for the college okay any value for the college
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so values so 102 s name
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saradi and branch ec so we are not passing any value for the college
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so still it was executed so previously okay previously
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if you give this one the default value for the college will be null but here
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while creating a table we are giving a constraint for the college attribute that is a default pc that means if you
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if any value is not passed here so automatically the default value for the college will be
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filled with vc you can observe here see
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we have not given any any college name for 102 roll number 102 but the college
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name is bc okay so if you are not mentioning here if you are not using any attributes here
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you you are supposed to pass the values see for example
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let us take here insert into student so i am not giving any value here i am
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passing only the three parameters so i will give some ramu and
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103 so it will give an error because the column count doesn't match value at count at row one so because four
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attributes are there here we are giving only the three attribute values so we have to pass the
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attribute i mean value for the attribute college also even though it was given a default pc
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so here we can skip that one so if you want to give only the values for a few attributes then you have to follow this
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syntax itself so automatically the default value given for this particular attribute will be set as a pc
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so you should not use this one okay for the default so if you are using this one you are
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supposed to give all values for all the attributes even though there is a default value
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right so hope you understood this one so this is all about our default
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and then the unique unique is similar to our primary key but
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but the it can be accepted in null value it can be accepted another value so let us
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check so let us drop the student detail so drop table student
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so yes system cls so show tables you can observe the empty
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set so create table student so with sid integer
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s name where care of 30 and some percentage
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right sorry let us take some roll number
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okay roll number of integer which is of a unique let us give the constraint unique so
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roll number will also be unique but or else we can give the contact number
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why don't we give the contact contact which is of a integer let us take the
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integer itself and give the unit so it's not a mandatory that every student
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will be having a contact number right so unique and let us check
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primary key with a s id execute so query okay zero rows affected
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so you can use show tables to check the details so dsc
39:52
student so which is a student okay you can see
39:58
unit key is a primary and this is a unique key now let us try to insert the values
40:03
insert into a student student let us take all the values
40:08
student values so one zero one so sandeep and the third one is a contact
40:14
number yes the contact number will be some one two three four five six seven
40:21
so query okay so you can check select star from student
40:26
so we got this one contact yes so let us check one more time
40:31
so insert into a student values and if if you are not able to give only the yes name
40:39
if you just want to give the s name so if you don't want to give the s
40:44
i mean s id and the contact number definitely will get an error because s id is a primary key it should be not
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null it should be not so let us take here
40:57
yes id and s name or or let us check with the
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multiple values so 1 0 102 and let us take this one
41:08
saradi and what is the contact number which we have given one two three four five six and seven
41:15
see so it will also be not not accepted because the contact number
41:21
is a duplicate value that means there is one more contact number here okay so here the contact is a unique the contact
41:28
attribute is a unique so it should also not accept the duplicate values
41:33
so that's why it was not accepted and one more thing rather than that it can accept the null
41:38
value it can accept the null value
41:44
student s id yes name so which gives the one zero two and sarah b so one draw
41:50
affected so you can see so select a star from student so it can be it can be null so that's
41:56
the only difference between the primary key and a unique key a primary key and a unique key
42:05
okay so uh that means a primary key and unique both are equal so it will it doesn't accept
42:12
the duplicate values but apart from the primary key unique will
42:17
accept the null value that's the only difference okay so this is a syntax how we can
42:23
give the unique constraint for any attribute
42:29
right so hope you understood this one right the next one a foreign key
42:40
so now foreign key we know that the foreign key means the primary key of one table will be the foreign key of another
42:46
table let us take the two tables so i will show you the syntax
42:51
how we can give the foreign key okay with the help of a foreign key itself we are going to
42:58
relate the tables right so let us create this one
43:09
so student table will create the student table with sid yes name
43:15
branch and course id and also
43:24
course table with course id and course name
43:29
and duration right so you can observe here course id is a primary key in course table which
43:37
is a foreign key in a student table which is a foreign key in student table
43:42
so let us create that one let us create this one so
43:48
create so let us clear the screen system cls
43:54
create table let us create the course table first course
44:00
cid of a integer and c name of
44:06
where care of 30 right only two two attributes we are
44:12
giving only two attributes and let us give the primary constraint primary key
44:19
as cid so query ok you can check show tables so we are having a
44:26
course table and a student table okay so let us drop here the student table and let us create one more student
44:33
table now let us check show tables will give
44:39
only the course table now we will create a student table with a course id
44:45
as a foreign key so create table student
44:51
okay what are the fields student id student name branch nci student
44:58
sid with the integer s name with the var care of
45:05
30 characters branch with a rare cap of
45:10
20 characters and cid with integer
45:16
integer right so also we have to give the primary key so primary
45:22
key is of sid and again we need to give the foreign key what's the foreign key
45:29
foreign key of the foreign key which is a foreign key here cid is a foreign key
45:37
which references which references the course
45:43
of cid so the foreign key is a cid in this table
45:49
which references to the primary key cid of course table right so this is the syntax
45:55
oh sorry references okay yes is uh
46:00
we have to give the references not a reference right sorry so let us click create table student
46:09
sid integer yes name where care of
46:16
30 branch where care of
46:21
20 cid of integer
46:26
primary key of sid
46:32
foreign key of cid references so here we have not given yes
46:39
okay so references cid of course that means which is of a
46:46
primary key so you can see query okay zero close affected now you can see
46:52
show tables so two tables course and student so you
46:59
can observe describe student you can see
47:05
see primary key and mul mul means nothing but is a foreign
47:10
key okay it's a foreign key right so describe course so here also
47:16
we'll get the structure which is a primary key which is a primary key right so this is how we can create a
47:22
foreign key okay so once again i'm explaining so this is the only creation of a foreign key and a primary key
47:29
constraints i am not inserting any values so we will discuss about the foreign key while executing the queries
47:36
relating with the different tables okay so but this is a syntax how we can
47:41
give the foreign key for any uh table okay any any attribute for any
47:47
attribute right so hope you understood this constraints so this is all about our
47:53
constraints a primary key not null check default unique and foreign
47:59
so let's let's stop here hope you understood this session so if you are having any doubts regarding this one
48:06
feel free to post your doubts in the comment section definitely i'll try to clarify all your doubts and if you
48:11
really enjoyed my session like my session share my session with your friends and don't forget to subscribe to
48:16
our channel thanks for watching thank you very much