GATE 2009 relational algebra, TLC

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Let R and S be relational schemes such that R={a,b,c} and S={c}. Now consider the following queries on the database:

1. πRS(r)−πRS(πRS(rsπRS,S(r))

 

2. {ttπRS(r)∧∀us(∃vr(u=v[S]∧t=v[RS]))}

 

3. {ttπRS(r)∧∀vr(∃us(u=v[S]∧t=v[RS]))}

 

4. 

Select R.a,R.b
    From R,S
    Where R.c = S.c

Which of the above queries are equivalent?

  1. 1 and 2
  2. 1 and 3
  3. 2 and 4
  4. 3 and 4

sir pls explain with  each option . i am not able to understand it properly.

asked Dec 28, 2016 in DBMS by mohit16 (670 points)

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