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Entity-Relationship Model Cont…..

Entity-Relationship Model Cont…. CST203-2 Database Management Systems Lecture 5. There are 2 formal languages for relational model Relational algebra Relational calculus. Relational Algebra. What is relational algebra? The result? Sequence of relational algebra Divided into 2 groups.

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Entity-Relationship Model Cont…..

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  1. Entity-Relationship ModelCont….. CST203-2 Database Management Systems Lecture 5

  2. There are 2 formal languages for relational model • Relational algebra • Relational calculus

  3. Relational Algebra

  4. What is relational algebra? • The result? • Sequence of relational algebra • Divided into 2 groups

  5. Special operations • Selection • Projection • Join • Rename • Set operations • Union • Intersection • Set difference

  6. Similar to normal algebra

  7. SELECT operation σσ<Selection Condition>(R) • σ – SELECT operator • Selection Condition : Boolean expression • R : relation • If more selection conditions, • Use ‘OR’, ‘AND’ and ‘NOT’

  8. Horizontal partition • Select the students who has the GPA greater than 3.5 σσGPA > 3.5 (STUDENT) Student Table

  9. +++++++++

  10. σ<Condition1>(σ<Condition2>(R)) = σ<Condition2>(σ<Condition1>(R)) σ<Cond1>(σ<Cond2>(σ<Cond3>(R))) = σ<Cond1> AND <Cond2> AND <Cond3>(R)

  11. Assignment • Write the relational algebra for selecting all details whose department is 4 and whose salary is greater than 30,000 • Write it in another way

  12. PROJECT operation • If want to choose a subset of the columns in a relation and discards the rest, • Use Π ΠName, GPA (Student) Π<attribute list>(R)) Π<list1>(Π<list2>(R))) = Π<list>(R))

  13. Assignment • Write the relational algebra for selecting Name, Eno, and Address

  14. Sequence of operations STU_1stCLASSΠname(σGPA > 3.5 (STUDENT))

  15. Assignment • Write the relational algebra for selecting Name, Eno, and Address of all male employees whose salary is greater than 20,000

  16. CARTESIAN PRODUCT

  17. INNER JOIN

  18. UNION operation Result 1 Πname(σGPA > 3.5 (STUDENT)) Result 2 Πname(σ(GPA > 2.5 AND GPA < 3.5) (STUDENT)) Result Result1 υ Result 2

  19. Result 1 • Result 2 • Result

  20. INTERSECTION operation Result 1 Πname(σGPA > 3.5 (STUDENT)) Result 2 Πname(σ(GPA > 2.5) (STUDENT)) Result Result1 Result 2 υ

  21. Result 1 • Result 2 • Result

  22. SET DIFFERENCE • Also called as MINUS Result Result1 – Result2

  23. Result 1 • Result 2 • Result

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