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Computer Science- CBSE CLASS XII

Q. 19. What do you understand by Primary Key and Alternate Key. Explain with example.                             For - 4 Marks

Ans : PRIMARY KEY : It is a set of one or more attributes that can uniquely identify tuples within the relation.
ALTERNATE KEY : A candidate key that is not the primary key is known as an alternate key.
For ex.
    Relation: Data

Here in above table EmpNo, MobileNo, PANCardNo & BankAccountNo are candidate keys. If EmpNo is made the primary key then remaining will automatically become alternate keys.

Q.20. Consider the following table GAMES and PLAYER. Write SQL commands for the statements (i) to (iv) and give outputs for SQL queries (v) to (viii).

Table : GAMES

Table : PLAYER

1. to display the details of those games which are having prize money less than 30000 and organized before 2009.                             For - 1 Marks

Ans. : SELECT * FROM GAMES WHERE PRZMONEY<30000 AND SCHDATE<’01-JAN-2009’ ;>

2. to display the name of PLAYERS in reverse alphabetical order.                             For - 1 Marks

Ans. : SELECT NAME FROM PLAYERS ORDER BY NAME DESC;

3. to increase the prize money by 1000 for those games which name starts with ‘B’.                             For - 1 Marks

Ans. : UPDATE GAMES SET PRZMONEY=PRZMONEY+1000 WHERE GAMENAME LIKE ‘B%’;

4. Insert an additional attribute namely DOB for entering date of birth in table PLAYER.                             For - 1 Marks

Ans. : ALTER TABLE PLAYER ADD(DOB DATE);

5. SELECT GAMENAME,NAME FROM GAMES G,PLAYER P WHERE G.GCODE=P.GCODE;                             For - 1 / 2 Marks

Ans. :    

GAMENAME	NAME
Chess	Rakesh Srivastava
Badminton	Niesh Mishra
Basketball	Vandana
Table Tennis	Ravi Jindal

6. SELECT MIN(SCHDATE), MAX(PRZMONEY) FROM GAMES ;                             For - 1 / 2 Marks

Ans. : MIN(SCHDATE)       MAX(PRZMONEY)
           ----------------------      ---------------------------

           12-Nov-2008         40000

7. SELECT AVG(PRZMONEY) FROM GAMES WHERE SCHDATE<’01-JAN-2009’;                             For - 1 / 2 Marks

Ans. :             AVG(PRZMONEY)
                       --------------------------

                           38000
8. SELECT COUNT(DISTINCT NUMBER) FROM GAMES;                             For - 1 / 2 Marks

Ans. :  COUNT(DISTINCT NUMBER)
           -----------------------------------------

              3

Prepared By: Mr. Pradumna Singh
mail to: [email protected]