conditional join, DBMS, projection operator

Question

why don't we use the projection operator in conditional join?

Comments

In conditonal join we combine attributes from two unknown table that is there is no possibilty of comon elements but in projection operator we use it to remove duplicates so here it is of no use...

Answer 1

Conditional Join is also known as theta join. It combines tuples from different relations provided they satisfy the theta condition.

Ex: R1 and R2 are relations having attributes (A1,A2...An) and (B1,B2,….Bn) such that attributes don’t have any thing in common, that is R1 (intersection) R2 = pie.

since there are no common things, there are no duplicates, without duplicates there is no use of using projection operator.