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Explain the relational algebra in DBMS?
Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.
Relational algebra
It is a procedural query language. It gives a step-by-step process to obtain the result of the query. It uses operators to perform queries.
Relational algebra can be depicted as follows −
Algebraic Operations
The different algebraic operations in the DBMS are as follows −
Let us understand the relational algebra operations in DBMS.
Select operation
It displays the records that satisfy a condition. It is denoted by sigma (σ). It is a horizontal subset of the original relation.
Syntax
σcondition(table name)
Projection operation
It displays the specific column of a table. It is denoted by pie (П). It is a vertical subset of the original relation. It eliminates duplicate tuples.
Syntax
Пregno(student)
Rename operation
It is used to assign a new name to a relation. It is denoted by ρ (rho).
Syntax
ρnewname (tablename or expression)
Union operation
Union operation combines values in R1, R2 removing duplicate ones.
Syntax
Пregno(R1) ∪ Пregno(R2)
It displays all the regno of R1 and R2.
Intersection operation
It displays the common values in R1 & R2 and is denoted by ∩.
Syntax
Пregno(R1) ∩ Пregno(R2)
Difference operation
It displays the value present in R1 but not in R2. It is denoted by –(minus).
Syntax
Пregno(R1) - Пregno(R2)
Cartesian product operation
It combines R1 and R2 without any condition and is denoted by X.
Degree of R1 XR2 = degree of R1 + degree of R2
{degree = total no of columns}
Join operation
It combines R1 and R2 with respect to a condition. It is denoted by ⋈.
Joins are of different types
Theta join.
Natural join.
Outer join − This is further classified into the following types −
Left outer join.
Right outer join.
Full outer join.
Division operation
The division operator is used for queries which involves the ‘all’
R1/R2 = tuples of R1 associated with all tuples of R2.
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