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32 votes
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SELECT operation in SQL is equivalent to

  1. The selection operation in relational algebra
  2. The selection operation in relational algebra, except that SELECT in SQL retains duplicates
  3. The projection operation in relational algebra
  4. The projection operation in relational algebra, except that SELECT in SQL retains duplicates
in Databases
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Best answer

Option D is correct because SELECT operation in SQL is equivalent to The projection operation in relational algebra, except that SELECT in SQL retains duplicates but projection gives only distinct. 


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11
@Arjun Sir: This question is an perfect example where GATE gets really tricky. Most will write Option B.

Now such questions really clear the concepts. This should be marked as tricky. I'd ask you to add one more tag apart from easy normal hard a TRICKY tag. there are tons of such tricky questions. Pondering over these would help a lot of Gate Aspirants.
19
Actually I wouldn't mark this as tricky as GATE has more trickier questions in store :)

But, whichever question you find like this, you can mark as "favorite" and this can be useful during exam time for quick reference.
0
any source/material for explanation!
1
Selection in relational algebra select rows and projection in RA select columns. Select operation in SQL selects columns but duplicates values are retained in SQL.
Answer:

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