unary operations in Relational Algebra ?

[joyadelfin]

Hello Dear,

Please Tell Me What are the unary operations in Relational Algebra ?

[shaili shah]

There is two types of unary operator select and project.
Select operation is like :
σDno=4 AND Salary>25000 (EMPLOYEE) is same like the sql select operation as
select * from EMPLOYEE where Dno =4 and Salary > 25000.

Project operation is like :
πSex, Salary(EMPLOYEE) is same like as
select Sex, Salary from EMPLOYEE.

But difference is select operation only select tuples where project operation select columns.

I hope you'll understand.

Thank you!