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Que. SQL allows tuples in relations, and correspondingly defines the multiplicity of tuples in the result of joins. Which one of the following queries always gives the same answer as the nested query shown below:

select * from R where a in (select S.a from S)
a. select R.* from R, S where R.a=S.a (D)
b. select distinct R.* from R,S where R.a=S.a
c. select R.* from R,(select distinct a from S) as S1 where R.a=S1.a
d. select R.* from R,S where R.a=S.a and is unique R
Answer:select R.* from R,(select distinct a from S) as S1 where R.a=S1.a
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