Given relations R(w,x) and S(y,z), the result of SELECT DISTINCT w, x FROM R,…

• FROM R, S creates a Cartesian product of R and S.

• For each tuple of R, it gets repeated once for every tuple in S.

• SELECT DISTINCT w, x removes duplicates from the final result.

Now, the result will be exactly same as R only if:

1. R has no duplicates
   → Otherwise DISTINCT may remove tuples.

2. S is non-empty
   → If S is empty, Cartesian product is empty → result ≠ R.

The number of tuples in S doesn’t matter as long as S is non-empty, because DISTINCT collapses repetitions back to R.