0:01	foreign
0:06	welcome back in this presentation we
0:09	will focus on the relational algebra
0:11	fundamental operation the second
0:13	operation which is the project operation
0:15	and we know basically there are six
0:18	fundamental operations in relational
0:20	algebra number one the select number two
0:23	project three Union four is a difference
0:26	five Cartesian product and the sixth one
0:29	is renamed and we are now going to focus
0:32	on the second relational algebra
0:34	operation the project let's see the
0:37	theoretical Basics about the project
0:38	fundamental operation and basically we
0:41	need to understand the difference
0:43
between select and project select
0:45
selects all the tuples then what about
0:48
project project selects all the values
0:51
but certain attributes or columns left
0:54
out say if you want all attributes go
0:57
for select if you want selected
0:58
attributes then go for project nowadays
1:02
when we see an example it will be easy
1:03
for you to understand so the operation
1:05
of project is it's going to return its
1:08
argument relation with certain
1:10
attributes left out say for example if
1:13
we are having five columns or five
1:15
attributes and the output that you want
1:17
only two attributes instead of five
1:19
attributes then we can go for project if
1:22
you go for select operation you will get
1:24
all five attributes but if our
1:26
requirement is only selected attributes
1:28
then we can go for this project
1:30
operation because this project operation
1:33
is going to return the argument relation
1:35
with certain attributes left out and
1:38
what type of operator is this is it a
1:40
unary operator or a binary operator like
1:42
select operator project is also a unary
1:46
operator whereas going to take only one
1:48
relation as an input so it's going to
1:50
take one relation as an input and it
1:53
produces the output relation where the
1:55
output relation is going to be having
1:57
certain attributes left out based on our
2:00
requirement
2:01
and select operator is denoted by the
2:04
lowercase Greek letter Sigma and what
2:07
about project project is denoted by the
2:10
uppercase Greek letter Pi and this is
2:13
the uppercase Greek letter Pi and this
2:16
pie represents project remember the
2:18
shortcut Sigma starts with s select
2:21
starts with yes so select mean Sigma
2:23
likewise Pi starts with p and project
2:26
starts with p so the shortcut is pi is
2:30
used for denoting the project operation
2:33
we know basically a relation is a set
2:36
and that is why whatever the concept we
2:38
see in the mathematical concept the set
2:40
that is also applicable for relations
2:42
because basically a relation is a set in
2:46
other words I would also refer any
2:48
relation is a set and what's the output
2:50
of this project the output is going to
2:52
be the relation with certain attributes
2:54
left out what about the duplicate values
2:56
basically when we have the duplicate
2:58
values in the result the duplicate
3:01
values or duplicate rows are eliminated
3:03
remember if we are getting two rows with
3:06
the same value in the output only one
3:08
will be listed and the duplicate value
3:10
will not be displayed in the result and
3:12
that's one of the important features
3:14
about project say for example if we are
3:16
retrieving instructor name and
3:17
instructor salary if there are two John
3:20
with the same salary and we will be
3:22
getting only one John's information and
3:25
the other John's information will be
3:26
discarded because it is a duplicate
3:28
value and project actually will not
3:31
display the duplicate rows then let's
3:33
see the syntax now the syntax is as
3:36
mentioned this is the uppercase Greek
3:37
letter Pi which is used to denote the
3:39
project operation in the subscript we
3:42
are going to retrieve only attributes if
3:44
we have 10 attributes in a relation and
3:46
we are going to retrieve only five
3:48
attributes just list what all the five
3:50
attributes we require attribute 1 comma
3:53
attribute 2 comma up to all the
3:55
attributes that we require from where
3:57
from the relation so the syntax is
4:00
project in the subscript Give the names
4:02
of the attribute that we require and
4:05
then give the relation name here when we
4:07
see an example then it will be easy for
4:09
us to understand let's take the same
4:11
instructor table which we have seen for
4:13
the select operation with the same
4:15
attributes and the same values
4:18
example number one list all instructors
4:21
ID name and salary but do not care about
4:25
the department name so what do you mean
4:27
by this though we have four attributes
4:30
in the instructor relation the ID name
4:31
Department name and salary we are
4:34
required to retrieve all instructors ID
4:36
name and salary and we don't want what
4:39
attribute the department name from the
4:41
output table or in the result table and
4:44
if you are sure about the syntax then
4:46
writing the query is easy the relational
4:48
algebra expression is
4:50
project what all the attributes we want
4:52
to project only ID because that is
4:55
required then name which is also
4:57
required and then the last one is salary
5:00
which is also required so we are going
5:01
to retrieve only ID name and salary
5:03
which is ID name and salary from which
5:07
relation the instructor relation there
5:09
is no condition we will be getting the
5:11
information about all the instructors
5:13
but with only one attribute left out
5:15
what is the attribute the department
5:17
name so the output is going to be all
5:20
the attributes except only one column
5:22
what is that column the department name
5:25
so the output is going to be ID name and
5:27
salary with no Department name and if
5:30
you note here what is the table name of
5:32
this output
5:34
there will be no table name no worries
5:36
when we see the last fundamental
5:37
operation the rename at the time I will
5:40
explain more about this table name for
5:42
now just understand the output is going
5:44
to be certain attributes left out
5:46
because we are talking about project
5:47
let's see one more example then it will
5:49
be easy for you to understand for this
5:52
example also I am going to take the same
5:53
instructor relation but with a different
5:55
question and the question is find the
5:58
name of all instructors in the computer
6:00
science department
6:02
what do you mean by this
6:04
we are going to list only the name of
6:07
all instructors in the previous case we
6:09
listed three attributes but here we are
6:11
going to list only name of all
6:13
instructors but there is a condition
6:15
mentioned the condition is the
6:18
instructor must be belonging to what
6:20
department computer science department
6:22
so in the department name attribute we
6:25
have two entries computer science for
6:27
Robin and computer science for project
6:29
so we want to list the names of all
6:33
instructors who are working for computer
6:35
science department only but still we
6:37
don't want all columns ID name
6:39
Department name and salary if that's the
6:41
case then it will be select but here
6:43
what we want
6:44
project right name but in Project we
6:47
can't give the condition so how to
6:49
handle this first we need to select all
6:52
the tuples that are matching the
6:53
condition Department name is equal to
6:55
computer science so for this we need
6:57
select and after select gives the
7:00
resultant table from that output we need
7:03
to retrieve only names nobody see the
7:05
output you will be able to understand
7:06
the solution is actually the first query
7:10
to be executed is we want to select all
7:13
the tuples from which relation
7:15
instructor relation which is matching
7:17
the condition Department name is equal
7:18
to computer science so what are the
7:21
tuples we will be getting here so the
7:22
tuples will be 1 2 1 2 1 Robin computer
7:25
science ninety thousand and seven six
7:28
nine eight five prateek computer science
7:30
89 000 so this portion I mean this inner
7:33
query will be giving two tuples and from
7:36
these two tuples we are going to
7:37
retrieve only name so what are all the
7:40
names will be getting Robin and pretty
7:42
so if you see the output the out output
7:45
is going to be only Robin and pratik
7:48
because we want the names of all
7:50
instructors in the computer science
7:52
department if you still need more
7:54
clarity don't worry about this now
7:56
anyway in the coming lectures we are
7:58
going to see more examples than
8:00
understanding select and project will
8:02
become so easy and that's it for the day
8:04
what we have seen we have seen about the
8:07
project fundamental operation in this
8:09
presentation and in the next
8:10
presentation we will focus on the union
8:12
fundamental operation in relational
8:15
algebra
8:16
I hope the session is informative and
8:18
thank you for watching
8:20
[Music]
8:20	[Applause]
8:22	[Music]