50 DBMS MCQs with Answers

Consider the following transactions with data items P and Q initialized to zero:

T1: read (P) ;
    read (Q) ;
    if P = 0 then Q : = Q + 1 ;
    write (Q) ;
T2: read (Q) ;
    read (P) ;
    if Q = 0 then P : = P + 1 ;
    write (P) ;

Any non-serial interleaving of T1 and T2 for concurrent execution leads to

Table A
Id   Name    Age
----------------
12   Arun    60
15   Shreya  24
99   Rohit   11


Table B
Id   Name   Age
----------------
15   Shreya  24
25   Hari    40
98   Rohit   20
99   Rohit   11


Table C
Id   Phone  Area
-----------------
10   2200   02  
99   2100   01

Consider the above tables A, B and C. How many tuples does the result of the following SQL query contains?

SELECT A.id 
FROM   A 
WHERE  A.age > ALL (SELECT B.age 
                    FROM   B 
                    WHERE  B. name = "arun") 

Database table by name Loan_Records is given below.

Borrower    Bank_Manager   Loan_Amount
 Ramesh      Sunderajan     10000.00
 Suresh      Ramgopal       5000.00
 Mahesh      Sunderajan     7000.00

What is the output of the following SQL query?

SELECT Count(*) 
FROM  ( ( SELECT Borrower, Bank_Manager 
          FROM Loan_Records) AS S 
          NATURAL JOIN ( SELECT Bank_Manager, Loan_Amount 
                         FROM Loan_Records) AS T );

Consider the following relational schema: 
 

Suppliers(sid:integer, sname:string, city:string, street:string)
Parts(pid:integer, pname:string, color:string)
Catalog(sid:integer, pid:integer, cost:real)

Consider the following relational query on the above database: 
 

SELECT S.sname
    FROM Suppliers S
        WHERE S.sid NOT IN (SELECT C.sid
                            FROM Catalog C
                            WHERE C.pid NOT IN (SELECT P.pid  
                                                FROM Parts P
                                                WHERE P.color<> 'blue'))

Assume that relations corresponding to the above schema are not empty. Which one of the following is the correct interpretation of the above query?
 

Let R₁ (a, b, c) and R₂ (x, y, z) be two relations in which a is the foreign key of R₁ that refers to the primary key of R₂ . Consider following four options. (a)Insert into R ₁ (b)Insert into R ₂ (c)Delete from R ₁ (d)Delete from R ₂ Which of the following is correct about the referential integrity constraint with respect to above?

How to express that some person keeps animals as pets?

A view of database that appears to an application program is known as

Which operation is used to extract specified columns from a table?

The relation schemas R₁ and R₂ form a Lossless join decomposition of R if and only if: (a) R₁ ∩ R₂ ↠ (R₁ - R₂) (b) R₁ → R₂ (c) R₁ ∩ R₂ ↠ (R₂ - R₁ ) (d)(R₂ → R₁) ∩ R₂

In functional dependency Armstrong inference rules refers to