0:01	foreign
0:07	welcome back in this presentation we are
0:10	going to focus on the relational algebra
0:12
rename operation we know basically there
0:16
are six fundamental relational algebra
0:18
operations the select project Union set
0:22
difference Cartesian product and rename
0:25
we have already seen the first five
0:27
fundamental operations in the previous
0:29
lectures now we are going to focus on
0:31
the last fundamental relational algebra
0:34
operation the rename operation the name
0:37
itself says that this is going to rename
0:40
renaming what whether it is a table or a
0:43
column let's see that now we know
0:45
basically a database is a collection of
0:48
relations and any relation in a database
0:50
will certainly have a name
0:52
so the first point is a straightforward
0:55
point that all the relations in the
0:57
database have names then what is the
0:59
need for renaming let's see that now
1:01
what is basically a relational algebra
1:04
it is a set of operations which is going
1:06
to take one or more relations as input
1:09
and going to generate a new relation as
1:12
the output so the input relations we are
1:15
going to refer with the name but what
1:17
about the output relation this output
1:19
relation will certainly not have a name
1:22
and that's what the second Point says
1:24
that the results of relational algebra
1:26
expressions do not have a name and hence
1:29
it is useful to be able to give them
1:32
names in simple terms when we write a
1:34
relational algebra expression obviously
1:36
the relational algebra expression will
1:38
be evaluated and finally we will be
1:40
getting a relation as an output and that
1:43
output relation will not have a name by
1:45
default and hence we want to give the
1:48
output of the result of the relational
1:49
algebra expressions with a name and that
1:52
is is why we are here in this
1:54
presentation the rename operation in
1:56
relational algebra and what type of
1:58
operator is this rename is it a unary
2:00
operator or a binary operator
2:03
this is basically a unary operation
2:05
because it's going to take only one
2:08
input what do we mean by this it's going
2:11
to take an expression as an input and
2:14
that relational algebra expression will
2:15
be giving an output and that output will
2:18
be a table obviously and that table is
2:21
fed as an input to this rename operation
2:23
and this rename will be assigning a name
2:26
when we see the syntax then it will be
2:28
easy for you to understand and what is
2:30
the symbol that is used to denote the
2:32
rename operation
2:33
this rename operation is denoted by the
2:36
lowercase Greek letter rho and let's see
2:39
the syntax now the syntax is rho to the
2:43
subscript of this operator row we are
2:45
giving X and we are giving an expression
2:48
here what is this expression this
2:51
expression is actually this relational
2:52
algebra expression so when this
2:55
relational algebra expression is
2:56
evaluated the output is going to be the
2:59
table so after evaluating this
3:01
relational algebra expression there will
3:03
be an output table here and this output
3:05
table will generally not have a name and
3:08
we are going to give a name to this
3:10
relational algebra expressions output
3:12
which is the result of the relational
3:13
algebra expression and this output table
3:16
is actually renamed as X so here x is
3:20
the new table name so what we have seen
3:23
the output of the relational algebra
3:25
expression is going to be a table and we
3:27
are assigning a name to that table by
3:29
using this rename operator the lowercase
3:32
Greek letter rho are we done with the
3:34
basics of rename no still we have few
3:36
more important points to be done let's
3:38
see those points now
3:41
a relation R itself is considered to be
3:44
a trivial relational algebra expression
3:46
what do we mean by this say it need not
3:49
be the case that this operator row
3:51
should be given with the expression I
3:54
mean the relational algebra expression
3:55
sometimes what we can do is we can
3:58
directly give the name of the table to
4:00
the rename operator and we can rename
4:03
the table with a new name so what do we
4:05
understand from this I'll go back to the
4:07
previous slide then I will explain it
4:08
will be easy for you to understand so we
4:11
have already seen about this where this
4:13
row is a rename operator and this is a
4:16
relational algebra expression it's not
4:18
mandatory that it should always be a
4:20
relational algebra expression we can
4:22
give a name of the table here and we can
4:25
rename that table name with a new name
4:27
called X so what do we mean by this is
4:30
we can rename a table with a new name as
4:33
well using this relational algebra
4:35
operator row
4:37
so what we understand here is a relation
4:40
R by itself is considered a trivial
4:42
relational algebra expression and that
4:45
is why we can give this r as an input to
4:47
the relational algebra operator row
4:49
because this relation R itself is
4:52
considered to be a trivial relational
4:54
algebra expression so when we consider
4:56
this relation R itself as a trivial
4:58
relational algebra expression what's the
5:00
outcome the outcome is the same rename
5:03
operation can be applied to a relation R
5:06
to get the same relation under a new
5:09
name that's what I told you so we can
5:11
use this operator to rename an existing
5:13
relation with a new name and I want to
5:16
recapture a point one more time which is
5:18
the results of the relational algebra
5:20
expressions do not have a name and hence
5:23
we can use this rename operator row to
5:25
rename the output of the relational
5:27
algebra expression because the output of
5:29
a relational algebra expression is going
5:31
to be a table we are clear that with the
5:33
rename operator row we can easily rename
5:35
an existing table with a new table name
5:38
but what about the attributes can we
5:40
rename the attribute names of the table
5:42
of course we can rename the attribute
5:45
names using this syntax the same
5:48
operator Row for renaming the expression
5:50
we can give this expression may be a
5:52
relational algebra expression or a table
5:54
directly and while renaming the new
5:57
relation name will be X or the new table
6:00
name will be X and can you see here A1
6:02
A2 up to a n are the new names of the
6:06
attributes and this expression may be a
6:08
relational algebra expression which
6:09
gives the table as the output or we can
6:12
give the table name directly whatsoever
6:14
let's assume this particular relation as
6:17
RT n what do we mean by this it means
6:20
there are n columns and we can also
6:22
rename all the columns or attributes
6:24
with the new name A1 A2 up to a n so
6:27
from this we can understand that rename
6:29
can be used to rename the table as well
6:32
as rename the attributes and coming to
6:34
the example for rename operation we have
6:37
already seen how to perform the
6:39
Cartesian product between relations and
6:41
we have seen how to perform the
6:42
depositor Cartesian product moreover
6:44
relation in the previous example and we
6:47
took the deposit to relation the
6:49
borrower relation and we got this output
6:51
I told you the output of this relational
6:53
algebra expression that we performed
6:55
right this is actually a relational
6:57
algebra expression this table I mean
7:00
this particular table will not be having
7:02
a name and we are required to give a
7:04
name to this relational algebra
7:06
operation I mean we want to give a table
7:08
name for this output relation how that's
7:12
the homework for you you might be
7:14
wondering I didn't solve any problem but
7:17
still I am asking you to directly go
7:18
with the homework no problem let's take
7:21
the same example we have seen in the
7:23
previous lecture in the previous lecture
7:25
we have found out the names of all
7:26
instructors in the physics department
7:28
together with the course IDs of all the
7:31
courses they thought the output is going
7:33
to be a relation without any name and we
7:35
want to assign a name that is we are
7:38
going going to name the resultant
7:39
relation as instructor underscore
7:42
physics simply ins underscore physics if
7:46
you are directly watching this lecture I
7:48
request you to watch my previous lecture
7:50
to understand how Cartesian product
7:52
works
7:53
we know the output relational algebra
7:55
expression which is this this is the
7:58
required output we have another way of
8:00
solving the same problem so here is the
8:02
output now what is the question this
8:05
output should be renamed with a new name
8:08
called ins underscore physics so from
8:10
this it's clear that the output is going
8:13
to be a relation with only two
8:15
attributes name and course ID and we are
8:18
going to rename this output relation
8:19
that is that relation which is
8:21
containing name and course ID with the
8:24
new name ins underscore physics
8:27
so I'm just bringing in the row
8:29
operators the relational algebra rename
8:31
operator and I am giving a new name in
8:34
the subscript which is INS underscore
8:36
physics and I am giving the entire
8:38
expression what we have seen here inside
8:41
this it means this output relation is
8:44
going to be renamed as ins underscore
8:47
physics in case we want to rename this
8:49
instructor relation as ins it's so
8:52
simple Row in the subscript ins give the
8:55
expression as instructor inside this so
8:58
what do we mean by this this instructor
9:00
relation will be renamed as ins before
9:02
we sign out let me go to the previous
9:04
slide
9:05
and what you are asked to do you are
9:07
required to rename the output of this
9:09
depositor cross moreover relation with a
9:12
new name I will give you the name let
9:14
the name be output relation so solve
9:18
this question and post your answers in
9:20
the comment section I hope you guys
9:22
enjoyed this presentation and thank you
9:24	for watching
9:26	[Applause]
9:28	[Music]