Relational algebra in dbms
- 1. Relational AlgebraRelational Algebra Relational Algebra is a procedural query language.Relational Algebra is a procedural query language. It consists of a set of operations that take one orIt consists of a set of operations that take one or two relations as input and produce a new relation astwo relations as input and produce a new relation as their resulttheir result.. Presented to:- presented by:-Presented to:- presented by:- Dr. Himanshu Hora Sir Shekhar Singh TomarDr. Himanshu Hora Sir Shekhar Singh Tomar MCA(III sem)MCA(III sem)
- 2. Fundamental Operation in Relational Algebra are: • Selection • Projection • Union • Set Difference • Cartesian Product • Join
- 3. SELECTION (σ) • The SELECT operator is σ (sigma) symbol Used as an expression to choose tuples that meet the selection condition… σ<selection condition>(R) -> Select operation selects tuples that satisfy a given predicate. Ex:- find all employees born after 1st Jan 1950: • dob σ '01/JAN/1950'(employee)
- 4. PROJECTION(∏ )Pi • ∏ (pi) symbol used to choose attributes from a relation. • This operator shows the list of those attributes that we wish to appear in the result and rest attributes are eliminated from the table. ∏ <attribute list>(relation)
- 5. SELECTION & PROJECTION Example Id Name Address Hobby 1123 John 123 Main stamps 1123 John 123 Main coins 5556 Mary 7 Lake Dr hiking 9876 Bart 5 Pine St stamps Id Name Address Hobby 1123 John 123 Main stamps 9876 Bart 5 Pine St stamps σ Hobby=‘stamps’(Person) Person ∏Name,Hobby(Person) Name Hobby John stamps John coins Mary Hiking Bart stamps
- 6. UNION (U) • UNION is symbolized by , and∪ includes all tuples that are in R or in S, eliminating duplicate tuples, therefore set R UNION set S would be expressed as: • RESULT R S← ∪
- 8. Set Difference Operator (R-S) • the MINUS operation includes tuples from one Relation that are not in another Relation and symbolized by the – (minus) symbol. Therefore R – S would be expressed as… • RESULT ← R – S
- 10. Intersection ( )∩ • The INTERSECTION operation on a relation A INTERSECTION relation B, is symbolized by R ∩ S, includes tuples that are only in R and S. • RESULT ← R ∩ S
- 12. Cartesian Product (RXS) • Creates a relation that has all the attributes of R and S, allowing all the attainable combinations of tuples from R and S in the result. The notation used is X. • C = R X S
- 14. JOIN • The JOIN operation is denoted by the R|X|S symbol and is used to compound similar tuples from two Relations into single longer tuples. • Join operation is generally the cross product of two relation. • The notation used is • R JOIN join condition S
- 15. JOIN Example
- 16. Types of join • Natural Join • Outer Join
- 17. Natural Join • The JOIN involves an equality test, and thus is often described as an equi-join. Such joins result in two attributes in the resulting relation having exactly the same value. A `natural join' will remove the duplicate attribute(s). • In most systems a natural join will require that the attributes have the same name to identify the attribute(s) to be used in the join. This may require a renaming mechanism. • If you do use natural joins make sure that the relations do not have two attributes with the same name by accident.
- 18. Outer Join There are three forms of the outer join, depending on which data is to be kept. • LEFT OUTER JOIN - keep data from the left-hand table • RIGHT OUTER JOIN - keep data from the right- hand table • FULL OUTER JOIN - keep data from both tables
- 19. LEFT & RIGHT OUTER JOIN Example Figure : OUTER JOIN (left/right)
- 20. Full OUTER JOIN Example Figure : OUTER JOIN (full)
- 21. Thank you