Relational Algebra

In: Computers and Technology

Submitted By Gurpreet258
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The relational algebra is a theoretical language with operations that work on one or more relations to define another relation without changing the original relation. Thus, both the operands and the results are relations; hence the output from one operation can become the input to another operation.
This allows expressions to be nested in the relational algebra. This property is called closure. Relational algebra is an abstract language, which means that the queries formulated in relational algebra are not intended to be executed on a computer. Relational algebra consists of group of relational operators that can be used to manipulate relations to obtain a desired result. Knowledge about relational algebra allows us to understand query execution and optimization in relational database management system.
Role of Relational Algebra in DBMS
Knowledge about relational algebra allows us to understand query execution and optimization in relational database management system. The role of relational algebra in DBMS is shown in Fig. 3.1. From the figure it is evident that when a SQL query has to be converted into an executable code, first it has to be parsed to a valid relational algebraic expression, then there should be a proper query execution plan to speed up the data retrieval. The query execution plan is given by query optimizer.
Relational Algebra Operations
Operations in relational algebra can be broadly classified into set operation and database operations. Unary and Binary Operations
Unary operation involves one operand, whereas binary operation involves two operands. The selection and projection are unary operations. Union, difference,
Cartesian product, and Join operations are binary operations:
Unary operation operate on one relation
Binary operation operate on more than one relation
Selection Operation
The selection operation works…...

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