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Given relations r(w, x) and s(y, z), the result of select distinct w, x from r, s is guaranteed to be same as r, provided
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- r has no duplicates and s is non-empty
- r and s have no duplicates
- s has no duplicates and r is non-empty
- r and s have the same number of tuples
- r has no duplicates and s is non-empty
Correct Option: A
Distinct keyword tells that it will give duplicate entries only once and if r has duplicate entries than it will not show them more than once which tells us that if answer is to be same as r then r should not have any duplicate entries.
Options (c) and (d) are completely wrong but in option (b) its also not necessary that s must also have no duplicate entries thus the answer is option (a).
