Chapter 11 Database Concepts Solutions
Question - 1 : - What is relation? Define the relational data model.
Answer - 1 : -
A relation is a table having atomic values, unique row and unordered rows and columns. The relational mode represent data and relationship among data by a collection of tables known as relation, each of which has a number of columns with unique names.
Question - 2 : - What are all the domain names possible in gender ?
Answer - 2 : -
Male and Female.
Question - 3 : - Give a suitable example of a table with sample data and illustrate Primary and Candidate Keys in it.
Answer - 3 : -
A table may have more than one such attribute/ group of attribute that identifies a row/tuple uniquely, all such attribute(s) are known as Candidate Keys. Out of the Candidate keys, one is selected as Primary Key,
Question - 4 : - Observe the following table carefully and write the names of the most appropriate columns, which can be considered as (i) candidate keys and (ii) primary key.
Answer - 4 : -
Candidate keys : Id, Product
Primary keys: Id
Question - 5 : - Observe the following table carefully and write the names of the most appropriate columns, which can be considered as (i) candidate keys and (ii) primary key :
Answer - 5 : -
Candidate keys : Code, Item Primary keys : Code
Question - 6 : - Define degree and cardinality. Based upon given table write degree and cardinality.
Answer - 6 : -
Degree is the number of attributes or columns present in a table.
Cardinality is the number of tuples or rows present in a table.
Patients Degree = 4
Cardinality = 5
Question - 7 : - Differentiate between the Primary key and Alternate key of a table with the help of an example.
Answer - 7 : -
Primary Key – A primary key is a value that can be used to identify a unique row in a table .
Alternate Key – An alternate key is any candidate key which is not selected to be the primary key.
Example:
So, (Bank Account Number, Aadhaar Number) is a candidate key for the table.
Aadhaar Number ” Primary key
Bank Account Number ” Alternate Key
Question - 8 : - Explain the concept of candidate keys with the help of an appropriate example.
Answer - 8 : -
Candidate key is a column or set of columns that can help in identifying records uniquely.
Example,consider a Table STUDENT
Here, AdminN0 & Roll N0 define Table uniquely.
Hence, they are candidate keys.
Question - 9 : - A table ‘customer’ has 10 columns but no row. Later, 10 new rows are inserted and 3 rows are deleted in the table. What is the degree and cardinality of the table customer
Answer - 9 : -
Degree = 10[no.of cols]
Cardinality = 10-3=7[no.of rows]
Question - 10 : - A table ‘student’ has 3 columns and 10 rows and another table ‘student 2’ has the same number of columns and 15 rows. 5 rows are common in both the tables. If we take union, what is the degree and cardinality of the resultant table ?
Answer - 10 : -
Degree-3
Cardinality – 30 = (20 + 15-5)