Relational algebra, Union Operations, Binary Operations, Difference, Cartesian product 

By Prof. Fazal Rehman Shamil
Last modified on May 27th, 2019

Relational algebra, Union Operations, Binary Operations, Difference, Cartesian product 

Relational algebra is a query language that processes one or more relations to define another relation.
The basic operation of relational algebra are as follows;
1.Unary operations
Selection, Projection
Operations which involve only one relation are called unary operations.
2.Binary operations:
Operations which involve pairs of relations are called binary operations.
Examples:
Union, Difference, Cartesian product

Selection operation:
Selection operator is Sigma∑
It acts like a filter operation on relations.
∑ c (R)
Returns only those tuples in R that satisfy condition C
Conditions:
Comparison operators = < > =
Logical operators

Name Office Dept Rank
Saleem 400 Cs Assistant
Junaid 220 Econ Lecturer
Ghafoor 160 Econ Assistant
Babar 420 Cs Assistant
Saleem 500 Fin associate
Table: EMP

Example
Select only those employees who are in cs department BUT NOT lecturer AND NAME IS NOT SALEEM
Solution:
∑ Dept = ‘cs’ AND-SYMBOL ¬(Rank=’lecturer’ AND-SYMBOL Name=’Saleem’)(Emp)

Example
Select only those employees who are not in the cs department or lecturer.
∑ ¬(Rank=’lecturer’ OR-SYMBOL Dept = ‘cs’)(EMP)

Example:
Select only those employers who are assistant or in the economics department
∑ rank=’assitant’ OR-SYMBOL Dept = ‘Economics’(EMP)
Example: Select only those employees with the last name Saleem who are assistant.
∑ Name=’Saleem’ AND SYMBOL Rank = ‘assistant’ (EMP)

Example:

select only those employees who are in the CS department
∑ Dept = ‘Cs’ (EMP)

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Prof.Fazal Rehman Shamil (Available for Professional Discussions)
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