Projection(ff): In relational algebra, a projection is a unary operation. The result of such projection is defined as the set obtained when the components Of the tuple R are restricted to the set {a1……an}. It discards (or excludes) the other attributes.
Selection( σ,): In relational algebra, a selection is a unary operation written as πaθb(R)πaθvor (R) where:
1. a and b are attribute names.
2. p is a binary operation in the set.
3. v is a value constant.
4. R is a relation.
The selection (R) selects all those tuples in R for which 9 holds between the a and the b
(b)
1. SELECT FROM EMPLOYEE ORDER BY DOJ DESC;
2. SELECT NAME, DESIGN FROM EMPLOYEE WHERE SGRADE – “S02” OR SGRADE = “SO3;
3. SELECT * FROM EMPLOYEE WHERE DOJ BETWEEN ’09-FEB-2006′ AND ’08- AUG -200%
4. INSERT INTO EMPLOYEE VALUES(109, “HARSH RAY”, “HEAD-IT.S02”, ’09-SEP- 2007′, ’21-APR-1983′);