0:02
[Music]
0:05
thank you
0:09
[Music]
0:11
Hello friends welcome back to our
0:13
channel so in today's session we'll
0:15
discuss about one more important topic
0:17
in dbms that is the keys and different
0:21
types of keys used in dbms so first let
0:24
us see the key what is meant by a key
0:29
so keys in
0:34
dbms
0:36
first let us see about the key what is
0:38
the key so we know that in the
0:40
relational database so the data is
0:42
represented in terms of rows and columns
0:45
so here the rows are considered as a
0:47
tuples and the column is considered as a
0:50
attributes so a key is
0:55
key is an attribute
0:59
attribute
1:01
or set of attributes or set off
1:05
attribute that means it may be a single
1:08
column or a multiple columns
1:11
to identify
1:15
identify
1:17
rows
1:19
uniquely so without any repetition in
1:22
order to identify the rows in order to
1:24
get the rows okay from the table so
1:29
this attribute or a set of attributes is
1:32
called the key so different types of
1:35
keys available in linear Miss
1:40
so first one is a Super Key
1:47
second one
1:52
candidate key
1:59
primary key
2:06
foreign key
2:16
alternate key
2:22
Unity
2:27
composite
2:29
so these are the different categories of
2:32
keys which we are going to use in our
2:34
relational database system
2:37
right so super key candidate key primary
2:39
key foreign
2:43
now we'll take one example so let us
2:46
have a one table and from the table
2:50
we'll identify these keys so what is
2:52
exactly the Super Key what is exactly
2:54
the candidate Keys what are the primary
2:56
keys and all these things will identify
2:58
in that particular table right so let us
3:01
see the example
3:03
so let us take this example the employee
3:05
table so in this employee table we let
3:08
us have uh let us assume that the table
3:11
consists of the following attributes ID
3:14
employee name
3:16
some employee identification there is a
3:18
other or SSN whatever it may be employee
3:21
salary employee contact the phone number
3:24
and employee email
3:26
right so among this table let us
3:29
consider the four rows we are having
3:31
some four rows now let us consider the
3:34
Super Key so what is a Super Key
3:40
so a Super Key is a key
3:43
or a set of I mean is an attribute or a
3:46
set of attributes that identify the
3:50
Rose uniquely so let us take this one
3:54
so if you consider employee ID so you
3:57
can see employee ID is a unique okay
3:59
employee ID is a unique there is no
4:01
repetition so we can identify the
4:04
complete row
4:06
with the help of employee ID
4:08
so the employee ID itself can be treated
4:12
as a Super Key and the second
4:15
with the help of a employee name
4:18
so you can observe employee name two
4:21
persons shares the same name Hari so by
4:25
using the employee name we can't get the
4:27
details of his employee Unity right if
4:31
you try if you are trying to retrieve
4:33
the data of a name hurry we will get a
4:36
two records
4:37
so with the single employee name we
4:40
can't identify the rows uniquely
4:43
coming to the employee other so every
4:46
person will be having a unique identity
4:48
unique identity right so by using this
4:53
employee author we can get the details
4:55
of a student uniquely because employee
4:58
other or employee identification the
5:01
identification given by the government
5:02
will not be shared among multiple people
5:05
right so every person will be having an
5:07
unique ID so by using the employee other
5:10
also we can get the data we can derive
5:12
the other attributes of a row so this
5:16
can also be the
5:23
similarly employee salary again you can
5:25
have salary two persons can have the
5:28
same salary multiple persons can share
5:30
the same salary so we can't consider
5:33
this one singlely okay and we employ
5:35
content so we definitely we can get the
5:38
details of an employee based upon the
5:40
content because it is also given
5:42
uniquely but
5:43
it's not mandatory to that every person
5:46
have the contact number right so
5:50
practically it's not possible because
5:52
nowadays everyone will be having the
5:54
four phone number right so but
5:57
they might might be entered in the table
6:00
or they might not be entered in the
6:02
table so based upon the employee contact
6:04
also we can't get the details of a
6:05
employee coming to the employee email
6:08
the same thing so email is also unique
6:11
but it's not mandatory that every person
6:14
should have the email
6:16
okay so we can't consider that employee
6:18
email a single link to identify the
6:22
complete rows now we can give the
6:24
combinations along with the employee ID
6:26
we can have the employee name based upon
6:29
these two we can retrieve the data so
6:32
the third one employee ID
6:36
and employee
6:39
name
6:40
so this is one category so one key set
6:43
of attributes next employee ID
6:47
a
6:48
employee ID with another so you can give
6:51
the combination also
6:53
so employee ID
6:55
with employee
7:00
other
7:02
employee ID with employee salary
7:07
employee ID along with
7:10
employee salary
7:14
employee ID with the employee contact
7:16
yes we can get the data
7:19
employee ID
7:21
with employee
7:24
contact
7:26
similarly employee ID with employee
7:28
email yes employee ID with employee name
7:32
and employee other employee ID with
7:34
employee name and employee salary so
7:37
like that every combination every
7:40
combination with this unique identity
7:42
can be considered can be considered as a
7:46
Super Key so that means it is a superset
7:49
of all the keys so from this super key
7:52
which will identify all the remaining
7:55
keys
7:56
right so that's why super key is a super
7:59
set of all the keys
8:01
right so all the combinations to
8:04
identify the rows uniquely will be comes
8:07
under this super key so it can be a
8:10
single key or a set of keys
8:13
single key or a set of keys so we can
8:16
give any combination which gives the
8:19
data which derives the data uniquely
8:21
from the table will be consider as a
8:24
super game so in this table there will
8:27
be a lot of super keys
8:29
now from this super key we have to find
8:33
out the candidate key
8:35
right so the second type of key is a
8:40
candidate key
8:46
candidate key
8:49
so in order to identify the candidate
8:51
key and these keys are also identified
8:53
from the super keys so here the
8:55
candidate keys are
8:59
minimal set
9:01
of Super Key can be considered as a
9:06
candidate key what's the minimal State
9:09
the employer ID
9:11
okay so from this table
9:15
employee ID
9:17
comma
9:18
employee other
9:24
employee order and here employee ID and
9:28
employee name so already we have given
9:29
employee ID so you should avoid this one
9:32
and employee ID and employee rather we
9:35
have already given this one we can
9:37
ignore employee ID employees heavily
9:40
ignore employee ID employee contact
9:42
ignore so we have to consider only the
9:45
minimal set from the Super Key without
9:48
any repetition
9:50
is called the candidate key so in this
9:53
example we'll be having only two
9:55
candidate kits that is employee ID and
9:58
employee other
9:59
okay other than this we don't have any
10:03
candidates from this super key
10:06
so from the Super Key itself we have to
10:08
identify the candidate key so candidate
10:12
key means a minimal set of a Super Key
10:14
so minimal State means minimum
10:16
combination okay so first we have to
10:18
consider a single single key after that
10:21
we can go with the combination of keys
10:23
that means the two set of two keys set
10:25
of three keys set of four Keys set of
10:27
five Keys Etc but it should not be
10:30
available in this particular candidate
10:32
so whatever the page we have written in
10:35
Super Key associated with this
10:37
particular employee ID will not be
10:39
accepted as a candidate similarly the
10:43
pairs in the Super Key where this
10:46
particular employee order is associated
10:48
will not be considered because these two
10:50
are already considered as a candidate
10:53
key so that's why we call it as a
10:55
minimal set of a Super Key minimal set
10:58
of a Super Key
11:00
so this is the candidate key the next
11:03
one is
11:05
primary key
11:10
primary key
11:12
so primary key means is a key that means
11:16
it can be a a normal attribute a single
11:19
attribute or a multiple attributes which
11:22
can identify the roles uniquely right
11:26
without any redundancy so that means we
11:29
are having some candidate case among
11:31
these candidates case you can select one
11:35
as a primary key any candid key can be
11:38
considered as a primary key so here we
11:41
are having a two candidate keys so that
11:43
means employee ID and employee other
11:46
right so among these two we can consider
11:49
any one as a primary key so you can
11:52
consider employee ID as a primary key
11:54
you can consider employee other as a
11:57
primary key or you can also consider the
11:59
combinations if any combinations are
12:01
there in the candidate key we can also
12:03
identify those combinations also
12:05
right so primary key it can be
12:12
any key
12:14
from
12:16
candidate keys
12:21
candidates kids right so that that must
12:24
be
12:26
ID
12:27
or
12:29
employee
12:32
identification right let it be some
12:35
other card or a water card okay so water
12:38
card is also unique identification so we
12:40
can consider that also as a a candidate
12:43
key and the primary key
12:45
now if you consider this employee ID
12:49
okay if you consider that employee ID so
12:52
what are the another ID another keys in
12:55
the candidate key will be considered as
12:57
a alternate keys
13:00
so our next one is
13:07
alternate Keys the next one is alternate
13:10
keys so accept the primary key all the
13:14
keys available in candidate key will be
13:16
considered as a alternate case
13:18
so
13:24
all
13:30
candle keys
13:33
except
13:39
all the candidate Keys except the
13:42
primary key will be considered as a
13:44
alternate keys that means in this
13:46
example if you consider employee ID as a
13:49
primary key you can consider employ
13:50
other as an alternate key if you
13:53
consider I employ other as a primary key
13:55
you can consider employee ID as a
13:57
alternate key so whatever the keys
14:00
available in candidate keys will be
14:02
considered as an alternate Keys except
14:04
the primary key because among those are
14:06
among those candidate Keys we are
14:08
selecting one key as a primary key so
14:10
automatically the remaining keys will be
14:12
alternate keys
14:14
okay and the last one is in sorry the
14:17
next one is a unit key
14:19
okay
14:21
I'll erase this one
14:29
Unity
14:32
so unique key means it is also similar
14:35
to our primary key but it can have the
14:40
null character it can accept the null
14:42
character so one constraint for this
14:44
primary key is it should not be
14:47
not a null the value should not null and
14:51
also it should not be updated it should
14:54
not be updated right so once you give
14:57
the other other number or employee ID so
15:01
in future it will not be change the
15:03
number will not be changed right such a
15:06
type of attribute we have to consider it
15:08
as a primary key and it short it should
15:10
not be given as a null it should not be
15:13
given as a null so there should be an
15:15
employee ID and there should be an
15:17
employee other number
15:19
and similarly unique key is similar to
15:21
primary key
15:24
similar to
15:29
primary key
15:31
having
15:33
null
15:35
having null so you can observe here
15:38
employee contact so every person will be
15:40
having a unique contact but
15:43
there is a possibility to have the null
15:45
so that's why we should not consider
15:47
this as a primary key so this will comes
15:49
under the unity similarly employee email
15:52
is also unique okay employee email is
15:56
also unique because every person will be
15:58
having a different email ID so one email
16:00
ID cannot be shared among different
16:02
people so it will be the unique identity
16:04
for the row but here also it accepts the
16:08
null null value so this will comes
16:10
another unique key so in this example
16:13
employee
16:15
contact
16:19
and
16:20
employee
16:22
email both will comes under this unique
16:26
keys so both we can identify the
16:28
complete records with the help of either
16:30
contact or email but it will also accept
16:33
a null character but the property of
16:35
primary key is it should not have the
16:37
national value it should not have the
16:39
null value and it should not be updated
16:42
it should not be updated
16:44
right so these are the unique Keys
16:47
primary key Etc etcetera alternate Keys
16:50
super Keys next one is a foreignty
16:59
foreign
17:16
key
17:18
so this foreign K is a key which is used
17:20
to relate one table with another table
17:25
so key
17:27
used to
17:29
relate
17:32
one table
17:34
with
17:35
another table
17:39
so this will be done with the help of
17:41
this foreign key this will be done with
17:43
the help of this product
17:45
so a key will be considered as a foreign
17:47
key which is which can be treated as a
17:51
primary key in another table
17:53
so in one table the key will be a
17:55
foreign key in another table the same
17:58
key will be considered as a primary key
18:00
so with that relation I mean with that
18:03
particular foreign key we are going to
18:05
relate two different tables for example
18:08
let us consider the employee table so
18:10
employee ID
18:12
similarly
18:14
employee name
18:17
and some Department ID
18:20
okay in which department the employee
18:22
belongs to so this let us have the short
18:25
table right so in order to just
18:28
understanding we'll take only three
18:30
attributes so employee ID employee name
18:33
and Department ID and there is a one
18:36
more uh table called a department so
18:39
Dept ID
18:42
DPT name
18:45
and some projects
18:48
some project
18:52
so this is a one more
18:55
table
18:57
this is a one more table and here you
18:59
can observe in this this Prime this
19:02
employee ID will be considered as a
19:05
primary key
19:07
and in this table Department ID can be
19:10
considered as a primary key
19:15
you can see
19:16
the same Department ID the same
19:19
attribute is available in this
19:21
particular employee table but it is not
19:23
a primary key here so this will be
19:26
considered as a foreign key
19:29
foreign key so the foreign key is an
19:33
attribute of one table
19:36
which is a primary key of another table
19:39
which is a primary key of another table
19:42
so by using this foreign key this rows
19:46
will be related to this particular table
19:48
one table will be related to another
19:50
table so that is called a foreign key so
19:53
in one table it is a foreign key in
19:54
another table is a primary key
19:57
right so these are all the different
20:00
types of keys used in dbms so first one
20:04
is a Super Key and from that super key
20:07
we have to derive the candidate keys and
20:09
from that candidate Keys we have to
20:10
select the primary key and apart from
20:13
the primary key all the remaining keys
20:15
of our candid keys will be considered as
20:17
a
20:17
alternate keys and the unique identifier
20:22
or a unique key I mean the key which
20:25
uniquely identifies the rows but
20:27
accepting the null value will be
20:29
considered as a unique key and
20:33
to relate one table with another we are
20:36
going to use a foreign key right so
20:38
primary primary key of one table will be
20:42
acting as a normal attribute that means
20:45
a foreign key as a in the another table
20:48
right so these are all the introduction
20:52
to all the keys different types of keys
20:54
which we will which are available in our
20:56
dbms
20:58
so hope you understood this Keys concept
21:01
so let us stop here and if you are
21:04
having any doubts regarding these keys
21:06
so feel free to post your doubts in the
21:08
comment section definitely I will try to
21:09
clarify all your thoughts if you really
21:11
enjoyed my session like my session share
21:14
my session with your friends and don't
21:15
forget to subscribe to our Channel
21:17
thanks for watching thank you very much