What is theta join explain?
Theta Join - The theta join operation is an extension to the natural-join operation which permits us to merge selection and a Cartesian product within a single operation. Consider relations r(R) and s(S), and let θ be a predicate on attributes in the schema R ∪ S. The theta join operation r θ s is described as follows:
r θ s = σθ (r x s)