Question

Replace the natural joins in the following expressions by equivalent theta-joins and projections: a)(R(a,b) ⋈S(b,c)) ⋈S.c>T.cT(c,d)?

Replace the natural joins in the following expressions by equivalent theta-joins and projections:

a)(R(a,b) ⋈S(b,c)) ⋈S.c>T.cT(c,d)?

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Answer #1

Theta join is given as :

R1 R2 where is the join condition specified explicitly. In NATURAL JOIN, join condition is not specified explicitly as it is understood that the Join condition is common attribute between them.

Here when R and S is NATURALLY joined, the joining condition is implicitly understood as R.b= S.b.

In theta join, we need to specify this explicitly.

Here the equivalent query after replacing NATURAL JOIN is

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