DBMS SUBJECT TEST

Question

Let Depositor and Lender be relational schemas such that Depositor = {a/c number, cname , balance, branch} and Lender ={loan_number ,cname, amount , branch}. 

Now consider the following queries on the database :

Query 1 : ( t | ∃D ∈Depositor ( t.cname = D.cname ) ∧  ∃L ∈Lender ( t.cname = L.cname ) ) 

Query 2 : ( ( πcname Depositor )  ∩ ( πcname  Lender ) ) 

Query 3 : Select cname from Depositor d where exists ( select * from Lender l where l.cname = d.cname ) ;

Which of the following is a false statement ?

1. Query 1 and Query 2 gives same result 
2. Query 2 and Query 3 gives same result 
3. Query 1 and Query 3 gives same result 
4. Query 1, Query 2 and Query 3 gives different results

Ans: 4
Doubt:
What will be the output of query 1
I think it will return only the tuples with only cname as column where D.cname  = L.cname(with no duplicates)
Output of query 2
Single column table containing cname where D.cname = L.cname(No duplicates)
Output of Query 3
Single column table containing cname where D.cname = L.cname(Containing duplicates)

PS: I’ll merge this with the original question when my doubts are cleared

Comments

mention that original question link too in your question itself !

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@Shaik Masthan i came through quite a lot of problems as  similar to Query3  but i never considered that duplicate ; 

but i think that the query will return duplicates too as it is sql query and moreover "Select distinct" is not used Here.

I want your opinion on this question

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this question was duplicate of https://gateoverflow.in/147567

i written answer there @newdreamz a1-z0

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