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013BSCCSIT002.docx - Join is a combination of a Cartesian...

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Joinis a combination of a Cartesian product followed by a selection process. AJoin operation pairs two tuples from different relations, if and only if a given joincondition is satisfied.We will briefly describe various join types in the following sections.Theta (θ) JoinTheta join combines tuples from different relations provided they satisfy the thetacondition. The join condition is denoted by the symbolθ.NotationR1θR2R1 and R2 are relations having attributes (A1, A2, .., An) and (B1, B2,.. ,Bn) suchthat the attributes don’t have anything in common, that is R1 ∩ R2 = Φ.Theta join can use all kinds of comparison operators.StudentSIDNameStd101Alex101
102Maria11SubjectsClassSubject10Math10English11Music11SportsStudent_Detail −Student_detailSIDNameStdClassSubject2
101Alex1010Math101Alex1010English102Maria1111Music102Maria1111SportsEquijoinWhen Theta join uses onlyequalitycomparison operator, it is said to be equijoin.

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Term
Fall
Professor
NoProfessor
Tags
Relational model, Tuple, Outer Joins, Join operation pairs

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