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Let r and s be two relations over the relation schemes R and S respectively, and let A be an attribute in R.  The relational algebra expression $\sigma_{A=a}(r \bowtie s)$ is always equal to

  1. $\sigma_{A=a}(r)$
  2. $r$
  3. $\sigma_{A=a}(r) \bowtie s$
  4. None of the above
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3 Answers

Best answer
42 votes
42 votes

Answer is C.

C is just the better form of query, more execution friendly because requires less memory while joining. query, given in question takes more time and memory while joining.

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23 votes
23 votes

 option c

8 votes
8 votes
Answer is (C).

It is an efficient way to write the query to select first the tuples then cross with other relation.
Answer:

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