Question

Which of the following statements are TRUE/FALSE?
S1: SQL permits attributes names to be repeated in the same relation
S2: The power of DRC and TRC is same as that of relational algebra
S3: The project operation (pi) cometimes only distributes over join (x) but not always

(A) <F,F,T>
(B) <F,T,T>
(C) <F,F,F>
(D) <T,F,T>

Sol.
I dont understand what it is meant by S3. I feel first two are false.

Answer 1

ans should be B (F,T,T)

first is surely false

second is true 

Just like TRC, DRC can also be written using existential and universal quantifiers. DRC also involves relational operators.

The expression power of Tuple Relation Calculus and Domain Relation Calculus is equivalent to Relational Algebra.

refer http://www.tutorialspoint.com/dbms/relational_algebra.htm

Project sometimes distributes over join (or product)

• If projlist can be split into separate lists, list1 and list2, so that list1 contains only attributes of R and list2 contains only attributes of S, then
• Π_projlist (R  S) = ( Π_list1 (R))  ( Π_list2 (S))
• referhttp://jcsites.juniata.edu/faculty/rhodes/dbms/queryopt.htm

Comments

S2 would be false.the power of DRC and TRC which will have  safe expression are equivalent to relational algebra but no safe term specified here

---

@Sanjay sir Is it true that S3 will be true only when list1 and list2 contains the primary key of R and S respectively(where Primary key of R referring the primary key of S).

---

Can you elaborate how S1 is surely false? I said first one may be false, but I still dont completely understand it. Now I am quite sure that S2 will be false and S3 will be true. But what S1 means?

---

@sanjay i think S2  is false because power of safe TRC is eqivalent to Relational algebra but it statement only say TRC which is either safe or unsafe plz check i am right or wrong