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Relational Algebra Operations (cont)

Theta Join
  • r ⋈C s   =   Join[C](r,s)   =
        { (t1 : t2)  |  t1 ∈ r ∧ t2 ∈ s ∧ C(t1 : t2) }, where r(R),s(S)
  • C is the join condition (involving attributes from both relations)
Computational view: 

result = {}
for each tuple t1 in relation r
   for each tuple t2 in relation s
      if (matches(t1,t2,C))
         result = result ∪ {concat(t1,t2)}