Database miscellaneous Easy Questions and Answers | Page - 15

Database miscellaneous

SQL allows duplicate tuples in relations, and correspondingly defines the multiplicity of tuples in the result of joins. Which one of the following queries always gives the same answer as the nested query shown below :
select * from R where a in (select S.a from S)
select R.* from R, S where R.a = S.a

1. select distinct R.* from R, S where R.a = S.a
1. select R.* from R, (select distinct a from S) as S1
1. where R.a = S1.a
1. select R.* from R,S where R.a = S.a and is unique R

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The one that give same answer is: select R. * from R, (select distinct a from S) as S1 where R.a = S1.

Correct Option: C

The one that give same answer is: select R. * from R, (select distinct a from S) as S1 where R.a = S1.

Consider the following relational schema: employee (empId,empName,empDept) customer(custId,custName,salesRepId,rating) salesRepId is a foreign key referring to empId of the employee relation. Assume that each employee makes a sale to at least one customer. What does the following query return?

1. Names of all the employees with at least one of their customers having a ‘GOOD’ rating.
1. Names of all the employees with at most one of their customers having a ‘GOOD’ rating.
1. Names of all the employees with none of their customers having a ‘GOOD’ rating.
1. Names of all the employees with all their customers having a ‘GOOD’ rating.

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NA

Correct Option: D

NA

Consider the following relation
Cinema (theater, address, capacity)
Which of the following options will be needed at the end of the SQL query
SELECT P1. address
FROM Cinema P1
Such that it always finds the addresses of theaters with maximum capacity?

1. WHERE P1. capacity >= All (select P2. capacity from Cinema P2)
1. WHERE P1. capacity >= Any (select P2. capacity from Cinema P2)
1. WHERE P1. capacity > All (select max(P2. capacity) form Cinema P2)
1. WHERE P1. capacity > Any (select max (P2. capacity) from Cinema P2)

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Inner query collects capacities of all the theatres and in outer query we are filtering the tuples with the condition “capacity>=All”. So the theatres which are having maximum capacity will be satisfy the conductivity and they will.

Correct Option: A

Inner query collects capacities of all the theatres and in outer query we are filtering the tuples with the condition “capacity>=All”. So the theatres which are having maximum capacity will be satisfy the conductivity and they will.

Consider the following relations :

Consider the following SQL query. SELECT S.
Student_Name, sum (P.Marks)
FROM Student S, Performance P
WHERE S.Roll_No. = P.Roll_No.
GROUP BY S.Student_Name
The number of rows that will be returned by the SQL query is _______.

1. 1
1. 2
1. 4
1. 25

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Output table is

Correct Option: B

Output table is

SELECT operation in SQL is equivalent to

1. the selection operation in relational algebra
1. the selection operation in relational algebra, except that SELECT in SQL retains duplicates
1. the projection operation in relational algebra
1. the projection operation in relational algebra, except that SELECT in SQL retains duplicates

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SELECT operation in SQL perform vertical partitioning which is made by projection operation in relational calculus, but SQL is multi-sets. Hence the projection operation in relational algebra, except that SELECT in SQL retains duplicates answer is correct.

Correct Option: D

SELECT operation in SQL perform vertical partitioning which is made by projection operation in relational calculus, but SQL is multi-sets. Hence the projection operation in relational algebra, except that SELECT in SQL retains duplicates answer is correct.