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Query is a question or requesting information. Query language is a language which is used to retrieve information from a database.

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 −

The different algebraic operations in the DBMS are as follows −

Let us understand the relational algebra operations in DBMS.

It displays the records that satisfy a condition. It is denoted by sigma (σ). It is a horizontal subset of the original relation.

σ_{condition}(table name)

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.

П_{regno}(student)

It is used to assign a new name to a relation. It is denoted by ρ (rho).

ρ_{newname}(tablename or expression)

Union operation combines values in R1, R2 removing duplicate ones.

П_{regno}(R1) ∪ П_{regno}(R2)

It displays all the regno of R1 and R2.

It displays the common values in R1 & R2 and is denoted by ∩.

П_{regno}(R1) ∩ П_{regno}(R2)

It displays the value present in R1 but not in R2. It is denoted by –(minus).

П_{regno}(R1) - П_{regno}(R2)

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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