Procedural language

1. Relational Algebra
 A procedural language which is used to access database
to read tables to read data in different ways.
 denoted using operators.
 each relational query describes a step by step procedure
for computing the desired answer, based on the order in
which operators are applied in the query.

2. Relational Algebra
 Operations:
 Selection
 projection
 Cartesian product
 Set Operations
Join

3. Relational Algebra
 Selection:
 to fetch rows or tuple from the table.
 syntax:
σpredicate(relation)
 predicate – logic using which the data from the relation is
selected.

4. Relational Algebra
 Ex: Student - Table
 σage>15(Student)
Reg. No Sname Age
1 AAA 15
2 BBB 18
3 CCC 16
Sname
BBB
CCC

5. Relational Algebra
 Projection:
 to project only a certain set of attributes of a
relation.
 remove duplicate data from the columns.
 Syntax: ΠA1,A2,…(r)

6. Relational Algebra
 Projection: Ex: Student - Table
 Πage(Student)
Reg. No Sname Age
1 AAA 15
2 BBB 18
3 CCC 16

7. Relational Algebra
 Cartesian product:
 to combine data from two different relations into
one and fetch data from the combined relation
Syntax: A x B

8. Relational Algebra
 Cartesian product: Example
Syntax: A1 x B1
Table A1
A B
1 1
2 2
Table B1
C D E
1 2 7
2 6 8
5 7 9
A1 x B1
A B C D E
1 1 1 2 7
1 1 2 6 8
1 1 5 7 9
2 2 1 2 7
2 2 2 6 8
2 2 5 7 9

9. • Set Operations
Union
Intersection
Set difference
Relational Algebra

10. Relational Algebra
 Union:
 to fetch data from two relations or temporary relation.
 the relations specified should have same number of
attributes and same attribute domain.
 duplicated tuples are automatically eliminated from
the result.
 Syntax: A ᴜ B

11. Relational Algebra
 Union: Example
Syntax: A1 ᴜ B1
Table A1
A B
1 1
1 2
2 1
Table B1
A B
1 2
2 3
A1 ᴜ B1
A B
1 1
1 2
2 1
2 3

12. Relational Algebra – Additional Operators
 Intersection:
 to fetch data from both tables which is common in
both the tables.
Syntax: A ∩ B

13. Relational Algebra
 Intersection: Example
Syntax: A1 ∩ B1
Table A1
Name id
aaa 1
bbb 2
ccc 1
Table B1
Name course
aaa C
ccc C++
A1 ∩ B1
Name
aaa
ccc

14. Relational Algebra
 Set-Difference:
 the result of set difference is tuples, which are
present in one relation but are not in the second
relation.
Syntax: A - B

15. Relational Algebra
 Set-Difference: Example
Syntax: A1 - B1
Table A1
A B
1 1
1 2
2 1
Table B1
A B
1 2
2 3
A1 - B1
A B
1 1
2 1

16. Relational Algebra
 Rename Operation:
 to rename the output relation for any query
relation which returns the result.
Syntax: ρ (RelationNew, RelationOld)

17. Relational Algebra
 Rename: Example
ρ (A1,B1)
Table A1
A B
1 1
2 2
Table B1
A B
1 1
2 2

18. Relational Algebra – Additional Operators
 Join:
 to fetch data from both tables which is common in
both the tables.
Operator: *

19. Relational Algebra
 Natural Join: Example
Syntax: A1* B1
Table A1
A B
1 1
1 2
2 1
Table B1
A C
1 2
2 3
A1 * B1
A B C
1 1 2
1 2 2
2 1 3