1. SELECT operation: SELECT operation is used to select tuples in a relation that satisfies a selection condition. Greek letter a (sigma) is used to denote the operation. Syntax – σcondition (relation) eg. σsalary>10000 (EMPLOYEE) – selects tuple whose salary is less than 10000 from EMPLOYEE relation.
2. PROJECT operation:
PROJECT operation selects certain columns from the table and discards the other columns. Greek letter7i(pi) is used to denote PROJECT operation.
Syntax – πcondition(relation)
eg. πname, salary(EMPLOYEE) displays only the name and salary of all employees
3. UNION operation:
This operation returns a relation consisting of all tuples appearing in either or both of the two specified relations. It is denoted by ∪. duplicate tuples are eliminated. Union operation can take place between compatible relations only, i.e., the number and type of attributes in both the relations should be the same and also their order.
e.g. SCIENCE ∪ COMMERCE gives all the tuples in both COMMERCE and SCIENCE.
4. INTERSECTION operation: This operation returns a relation consisting of all the tuples appearing in both of the specified relations. It is denoted by ∩. It can takes place only on compatible relations. e.g. FOOTBALL ∩ CRICKET returns the players who are in both football and cricket teams.