0:01	foreign
0:07	welcome back in this presentation we are
0:10	going to focus on the relational algebra
0:12	the assignment operation we know
0:15	basically there are six fundamental
0:17	relational algebra operations and few
0:19	additional operations and the additional
0:22	operations include the set intersection
0:24	operation the assignment operation the
0:27	natural join the division operation and
0:30	the outer join operation and the outer
0:33	join includes the left outer join right
0:35
outer join and the full router join
0:37
operation in this presentation we are
0:40
going to focus on the assignment
0:42
operation why do we need this assignment
0:45
operation that's what we are going to
0:47
see in this presentation basically this
0:49
assignment operation is similar to the
0:52
assignment operator in the programming
0:54
languages let's take any programming
0:57
language C or C plus plus Java or python
1:00
in any programming languages when we
1:02
wanna assign some value to a variable we
1:05
will be using the assignment operator in
1:08
most of the cases is equal to symbol is
1:10
used as the assignment operator let's
1:13
take a is equal to 10 what do we mean by
1:15
this we are assigning the value or the
1:18
constant 10 to the variable a we will
1:21
also do like this right a is equal to B
1:24
in this case the value of B is assigned
1:27
to a so simply assignment operators are
1:30
required in order to do assignments in
1:33
relational algebra also the assignment
1:35
operation is not an exception this is
1:38
also going to do the assignment like the
1:40
same assignment operator does in the
1:42
programming languages now what is the
1:44
symbol that is used to do this
1:46
assignment in some conventions they use
1:49
is equal to symbol and in some
1:51
convention they use the arrow and this
1:53
is a left Arrow so what it denotes is
1:56
the right hand side value is going to be
1:58
assigned to the left hand side so from
2:00
this it's clear that the assignment is
2:02
going to be made from the right hand
2:04
side to the left hand side and what type
2:06
of operator is this assignment operator
2:08
whether it is a unary operator or a
2:10
binary operator the assignment needs the
2:12
left hand side as well as the right hand
2:14
side so obviously this is also a binary
2:17
operator where it involves two operands
2:20
and hence assignment operation in
2:22
relational algebra will also come under
2:24
binary operator category so it's clear
2:26
that the assignment operator is going to
2:28
do assignment now we are going to see
2:31
what does this assignment is for
2:32
actually when we do some assignment the
2:36
database might be modified if the
2:38
assignment to a permanent relation is
2:40
made so what this point says is that
2:43
when we are referring a database and
2:45
when we are doing some assignment always
2:47
prefer this assignment to a temporary
2:50
relation name or a temporary relation
2:52
variable if we attempt to make an
2:54
assignment to a permanent relation then
2:56
obviously the database will be modified
2:58
because what we are doing we are trying
3:01
to change or modify the permanent
3:03
relation not a temporary relation what
3:06
do we mean by permanent and temporary
3:07
relation a permanent relation is the
3:09
relation that actually exists in the
3:11
database and we don't want that
3:13
modification to be carried out directly
3:15
on the database right then what about
3:17
temporary relations generally the output
3:20
of the relational algebra expressions
3:22
are the temporary relations and if we
3:24
want to assign it to a table name or if
3:26
we want to assign it to some variables
3:28
then we can go for this assignment
3:30
operator I know things will be unclear
3:33
at this stage when we see some examples
3:35
then it will be easy for you to
3:36
understand for now just understand the
3:39
database might be modified if the
3:41
assignment to a permanent relation is
3:43
made and what about the temporary
3:46
relation yes it is recommended so this
3:48
assignment operation is useful in the
3:51
situation where it is required to write
3:53
relational algebra expressions by using
3:56
temporary relation variables and we are
3:58
clear that the output of the relational
4:00
algebra expressions are tables or
4:03
relations and those output relations
4:05
will not have a name and when we want
4:07
the output of the relational algebra
4:09
expressions which are basically the
4:11
tables to a temporary relation variable
4:13
then we can go for the assignment
4:16
operator don't worry about this I will
4:18
give you an example say in this example
4:20
I am performing R intersection s we know
4:23
intersection is one of the additional
4:25
relational algebra operators which is
4:28
also a binary operator which takes two
4:30
inputs R and S and the output of this R
4:33
intersection s is going to be a relation
4:35
only and this relation is a temporary
4:38
relation and this output is obviously a
4:41
relation and we are storing the output
4:44
to relation variable p and this relation
4:47
variable p is actually a temporary
4:49
relation variable can you see here this
4:52
is a temporary relation variable and
4:55
that's what the previous Point says this
4:57
assignment operator is actually useful
4:58
in the situation where it is required to
5:01
write relational algebra expressions by
5:03
using temporary relation variable if you
5:05
ask me a question does it actually
5:07
enhance the power of relational algebra
5:09
like the other operators does I would
5:12
say no this assignment operator does not
5:15
provide any additional power to the
5:18
relational algebra apart from storing
5:20
the output of the relational algebra
5:22
expressions if that is the case then why
5:24
do we need this it has one advantage
5:27
because these assignment operators
5:29
provides a convenient way to express
5:31
complex queries so if you are writing
5:34
some complex queries and we need not
5:36
repeatedly write the complex queries
5:37
again and again what we can do instead
5:39
we can store it into a temporary
5:41
relation variable and we can start using
5:43
the temporary relation variable so that
5:45
it becomes easy and convenient to
5:48
express complex queries in relational
5:49
algebra let's see some examples here
5:52
what we are doing is we are writing a
5:54
complex relational algebra expression
5:56
and obviously the output of this complex
5:58
relational algebra expression is going
6:00
to be a table and we are going to store
6:02
that output in a relation variable temp
6:05
1 and if we have another expression like
6:07
Expression 2 which is also another
6:09
relational algebra expression and I am
6:11
storing the output of this in temp 2.
6:13
now expression 1 and Expression 2 just
6:16
imagine they are complex relational
6:18
algebra expressions which involves two
6:20
or three or more lines those complex
6:23
queries can be simply referred as temp 1
6:25
and tame 2 accordingly and we know temp
6:28
one and temp 2 are already the output of
6:30
this relational algebra expressions now
6:32
what we can write is the result can be
6:34
for example temp 1 divided by temp two
6:37
see how easily I am representing because
6:39
temp one may be a complex relational
6:41
algebra expression temp 2 may also be a
6:44
complex relational algebra expression
6:45
now I am just referring the temporary
6:47
relation variables temp 1 and temp 2 for
6:50
carrying out my task as mentioned is
6:52
equal to symbol may be used for
6:54
representing the assignment operation
6:56
there are some conventions which uses
6:58
this left Arrow say for example here the
7:01
Cartesian product between the two
7:02
relations R and S are actually stored in
7:05
temp one which is a temporary relation
7:08
variable and let's take another example
7:10
temp 2 which is actually representing
7:13
the output of this relational algebra
7:15
expression let's say the output is going
7:17
to be the projection of our Union Yes
7:19
from temp 2. say such complex queries
7:22
can be easily expressed using the
7:24
temporary relation variables by
7:26
assigning the values or by assigning the
7:28
complex queries to the temporary
7:30
relation variables so this is how these
7:33
assignment operators become handy
7:35
and that's it guys in this presentation
7:38	we have focused on the assignment
7:39	operation in the next presentation we
7:42	will focus on the natural joint which is
7:44	one of the important Concepts in
7:46	relational algebra I'll see you in the
7:48	next presentation and thank you for
7:50	watching
7:51	[Music]
7:51	[Applause]
7:54	[Music]
8:00	thank you