UNIT 2 relational algebra and Structured Query Language
- 1. Database Management System (DBMS) Sanjivani Rural Education Society’s Sanjivani College of Engineering, Kopargaon-423603 (An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune) NACC ‘A’ Grade Accredited, ISO 9001:2015 Certified Department of Information Technology (NBA Accredited) SY IT Prof. R. N. Kankrale Assistant Professor
- 3. Relational Algebra • Relational Algebra is a procedural query language which takes a relation as an input and generates a relation as an output. • Following are the important characteristics of relational operators- Relational Operators always work on one or more relational tables. Relational Operators always produce another relational table. The table produced by a relational operator has all the properties of a relational model. DBMS – Unit-II Relational Algebra Department of Information Technology
- 4. Relational Algebra Operators- DBMS – Unit-II Relational Algebra Department of Information Technology
- 5. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Selection Operator- •Selection Operator (σ) is a unary operator in relational algebra that performs a selection operation. •It selects those rows or tuples from the relation that satisfies the selection condition. Syntax- σ<selection_condition>(R)
- 6. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Examples- • Select tuples from a relation “Books” where subject is “database” σsubject = “database” (Books) • Select tuples from a relation “Books” where subject is “database” and price is “450”. σsubject = “database” price = “450” ∧ (Books) • Select tuples from a relation “Books” where subject is “database” and price is “450” or have a publication year after 2010 σsubject = “database” price = “450” year >”2010″ ∧ ∨ (Books)
- 7. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Important Points- Point-01: We may use logical operators like , , ! and relational operators like = , ≠ , ∧ ∨ > , < , <= , >= with the selection condition. Point-02: •Selection operator only selects the required tuples according to the selection condition. •It does not display the selected tuples. •To display the selected tuples, projection operator is used.
- 8. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Point-03: •Selection operator always selects the entire tuple. It can not select a section or part of a tuple.
- 9. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Projection Operator- • Projection Operator (π) is a unary operator in relational algebra that performs a projection operation. • It displays the columns of a relation or table based on the specified attributes. Syntax- π<attribute list>(R)
- 10. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Example-Consider the following Student relation- ID Name Subject Age 100 Ashish Maths 19 200 Rahul Science 20 300 Naina Physics 20 400 Sameer Chemistry 21
- 11. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Example-Consider the following Student relation- Result for Query πID , Name(Student)- ID Name 100 Ashish 200 Rahul 300 Naina 400 Sameer
- 12. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Important Points-Projection Operator- Point-01: •The degree of output relation (number of columns present) is equal to the number of attributes mentioned in the attribute list. Point-02: •Projection operator automatically removes all the duplicates while projecting the output relation.
- 13. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Point-03: •Selection Operator performs horizontal partitioning of the relation. •Projection operator performs vertical partitioning of the relation.
- 14. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Point-04: •There is only one difference between projection operator of relational algebra and SELECT operation of SQL. •Projection operator does not allow duplicates while SELECT operation allows duplicates. •To avoid duplicates in SQL, we use “distinct” keyword and write SELECT distinct. •Thus, projection operator of relational algebra is equivalent to SELECT operation of SQL.
- 15. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Set Theory Operators- 1.Union Operator ( ) ∪ 2.Intersection Operator (∩) 3.Difference Operator (-)
- 16. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology 1.Union Operator ( ) ∪ Let R and S be two relations. Then- •R S is the set of all tuples belonging to either R or S or both. ∪ •In R S, duplicates are automatically removed. ∪
- 17. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology Union Operator ( ):- ∪ Example- Consider the following two relations R and S- ID Name Subject 100 Ankit English 200 Pooja Maths 300 Komal Science Relation R ID Name Subject 100 Ankit English 400 Kajol French ID Name Subject 100 Ankit English 200 Pooja Maths 300 Komal Science 400 Kajol French Relation R S ∪ Relation S
- 18. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology . Intersection Operator ( )- ∩ Let R and S be two relations. Then- •R ∩ S is the set of all tuples belonging to both R and S. •In R ∩ S, duplicates are automatically removed.
- 19. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology . Intersection Operator ( )- ∩ Example-Consider the following two relations R and S- ID Name Subject 100 Ankit English 200 Pooja Maths 300 Komal Science Relation R ID Name Subject 100 Ankit English 400 Kajol French 100 Ankit English Relation S ID Name Subject 100 Ankit English Relation R S ∩
- 20. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology 3. Difference Operator (-)- Let R and S be two relations. Then- •R – S is the set of all tuples belonging to R and not to S. •In R – S, duplicates are automatically removed.
- 21. Relational Algebra DBMS – Unit-II Relational Algebra Department of Information Technology 3. Difference Operator (-)- Example-Consider the following two relations R and S- ID Name Subject 100 Ankit English 200 Pooja Maths 300 Komal Science Relation R ID Name Subject 100 Ankit English 400 Kajol French Relation S ID Name Subject 200 Pooja Maths 300 Komal Science Relation R – S
- 22. CARTESIAN PRODUCT • A Cartesian Join or CROSS JOIN returns the Cartesian product of two tables, meaning each row from the first table is combined with every row from the second table. This type of join does not require any specific condition or matching column between the two tables.
- 23. References • https://www.gatevidyalay.com/relational-algebra-relational-algebra-i n-dbms/ DBMS – Unit-II Relational Algebra Department of Information Technology