Lecture on Project Operation
Content covered: 

Working of PROJECT operation in Relation Algebra

  • Select and Project are unary operations, that works on a single relation.
  • Select and Project are commutative in nature.
  • Example:
    ID Name CGPA

    2

    B 9.6
    3 C 9.2
    7 B 9.8
  • Q: Select name of students whose CGPA is greater than 9
    A:σnameCGPA>9(Student)]
  • Resulting table :
    Name
    B
    C
  • Note:In a set there is no repetition of elements.
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3Comments
Rishabh Sharma @imrishabhsharma 23 Oct 2014 01:46 am

u said project ans select are commutative ...but if we do project frist thn relation givens only name ...now how could we apply condition over there for cgpa??

Pritam Prasun @pritam 23 Oct 2014 08:19 am

Thank You Rishabh, You have correctly pointed out the mistake. We can use both the operation only if we are not discarding some attribute which is used by later operations.

Rishabh Sharma @imrishabhsharma 24 Oct 2014 12:06 am

yes got the point....