DATABASE MANAGEMENT SYSTEMS

PRESENT BY:RUSHIT BHADANIYA

RELATIONAL ALGEBRA Introduction Join Operation

INRODUCTION Relational Algebra is a procedural query

language. It consists of a set of operations that

take one or two relations as input and produce a new relation as their result.

FUNDAMENTAL OPERATION IN RELATIONAL ALGEBRA ARE: Selection Projection Union Set Difference Cartesian Product Join

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

TYPES OF JOIN Theta Join Equi Join Natural Join Outer Join

EQUI JOIN For whatever JOIN type (INNER, OUTER, etc),

if we use ONLY the equality operator (=), then we say that the JOIN is an EQUI JOIN

THETA JOIN This is same as EQUI JOIN but it allows all

other operators like >, <, >= etc.

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 attributes.

EXAMPLE

OUTER JOINThere 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 and if there are no columns matching in the right table, it returns NULL values.

RIGHT OUTER JOIN - keep data from the right-hand table and If there are no columns matching in the left table, it returns NULL values.

FULL OUTER JOIN - keep data from both tables and it returns row from either table when the conditions are met and returns NULL value when there is no match.

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