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Computer Science 2 Marks Each

Database Query Using–SQL · CBSE STD 12 Commerce (CBSE - English Medium). 9 questions.

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9 questions · timed · auto-graded

Question 12 Marks
Differentiate between Candidate Key and Primary Key in context of RDBMS.
Answer
Candidate Key: All such attributes/columns, which can uniquely identify each row/record in a table

Primary Key: An attribute/column among the Candidate Keys which is used to uniquely identify each row/record in a table

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Question 22 Marks
What is the importance of a Primary Key in a table? Explain with a suitable example.
Answer
The Primary Key is an attribute/set of attributes that identifies a tuple/ row/ record uniquely.

Example:

Rollnumber in the table STUDENT

OR

AccessionNumber in the table LIBRARY

OR

EmpNumber in the table EMPLOYEE

OR

PanNumber in the table INCOMETAX OR

MemberNumber in the table MEMBER OR

AccNumber in the table BANK

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Question 32 Marks
Differentiate between the terms primary key and alternate key.
Answer
Primary Key: An attribute/ column used to identify each record in a table

Alternate Key: All such attributes/columns, which can act as a primary key but are not the primary key in a table.

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Question 42 Marks
Write the full form of DDL and DML?
Answer
DDL – Data Definition Language

DML – Data Manipulation Language

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Question 52 Marks
What is an Alternate Key?
Answer
Candidate key(s), which is not selected as Primary Key, is known as Alternate key(s).
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Question 62 Marks
Observe the following table CANDIDATE carefully and write the name of the RDBMS operation out of

(i) SELECTION (ii) PROJECTION (iii) UNION (iv) CARTESIAN PRODUCT, which has been used to produce the output as shown in RESULT ? Also, find the Degree and Cardinality of the RESULT.

Answer
(i) Selection and (ii) Projection

Degree = 2

Cardinality = 1

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Question 72 Marks
Observe the following STUDENTS and EVENTS tables carefully and write the name of the RDBMS operation which will be used to produce the output as shown in LIST ? Also, find the Degree and Cardinality of the LIST.

Answer
Cartesian Product

Degree of LIST = 4

Cardinality of LIST = 6

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Question 82 Marks
Observe the following tables VIDEO and MEMBER carefully and write the name of the RDBMS operation out of

(i) SELECTION (ii) PROJECTION (iii) UNION (iv) CARTESIAN PRODUCT, which has been used to produce the output FINAL RESULT as shown below, Also, find the Degree and Cardinality of the final result.

Answer
(iv) CARTESIAN PRODUCT

DEGREE = 5

CARDINALITY = 9

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Question 92 Marks
Write the difference between WHERE and HAVING clause.
Answer
Where clause is used for selecting the rows based on the condition applied on rows. While HAVING clauses used to
select the rows from the data given by group by group by clause in SQL.
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2 Marks Each - Computer Science STD 12 Commerce Questions - Vidyadip