# Relation algebra

May 29th, 2015
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Relation algebra consists of a set of operations that take one or two relations as input and produce a new relation as their results.Relatin algebra is procedural language

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Relation algebraRelation algebra consists of a set of operations that take one or two relations as input and produce a new relation as their results.Relatin algebra is procedural languageSix basic operatorsselect: s project: union: set difference: Cartesian product: xrename: r Fundamental RelationalThe select,project And rename operations are called unary operations,because they operate on one relation.The other set difference,Cartesian product,union are operate on pairs of relations and are therefore called binary operations.Unary OperationsThe Select OperationsThe select operations select tuples that satisfy a given predicate.Select is denoted by lowercase Greek letter sigma(s ),with the predicate appearing as a subscriptNotation-s p(r)Example-To select those tuples of the relation Employee whose city is Mumbai.scity=Mumbai (Employee)We combine several predicates into a larger predicates by using the connectives (and), (or), (not)Example- To select those tuples of the relation Employee whose city is Mumbai and empid is 10scity=Mumbai empid=10 (Employee)The Project OperationsThe project operation is a unary operation that returns its argument relation,with certain attributes left out.Project is denoted by lowercase Greek letter pi()We list those attributes that we wish to appear in the result as a subscript to Notation-attribute1,attribute2attributen(Relation)Example-To list only

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