(a) What is the difference between Candidate key and Alternate key? (b) What is the degree and cardinality

Q.

(a) What is the difference between Candidate key and Alternate key?

(b) What is the degree and cardinality of a table having 10 rows and 5 columns?

(c) For the given table, do as directed:

Table: STUDENT

 
 
 
	 
ColumnName
 
	 
DataType
 
	 
size
 
	 
Constraint
 
 
 
	 
ROLLNO
 
	 
Integer
 
	 
4
 
	 
Primary Key
 
 
 
	 
SNAME
 
	 
Varchar
 
	 
25
 
	 
Not Null
 
 
 
	 
GENDER
 
	 
Char
 
	 
1
 
	 
Not Null
 
 
 
	 
DOB
 
	 
Date
 
	 

 
	 
Not Null
 
 
 
	 
FEES
 
	 
Integer
 
	 
4
 
	 
Not Null
 
 
 
	 
HOBBY
 
	 
Varchar
 
	 
15
 
	 
Null
 
 
 
 

(i) Write SQL query to create the table.
(ii) Write SQL query to increase the size of SNAKE to hold 30 characters.
(iii) Write SQL query to remove the column HOBBY.
(iv) Write SQL query to insert a row in the table with any values of your choice that can be accommodated there.

Answer =

(a)
Candidate key: - All attribute combinations inside a relation that can serve as primary key are candidate key as these are candidates for primary key position.

Alternate key:- A Candidate key that is not primary key, is called an alternate key.

(b)

Number of:-
Degree: 5
Cardinality: 10

(c)

(i)

Create table STUDENT (
ROLLNO Integer(4) Primary Key ,
SNAME Varchar(25) Not Null,
GENDER  char(1) Not Null,
DOB date Not Null,
FEES  int(4) Not Null
HOBBY Varchar(15)
 ) ;

(ii)

Alter table STUDENT modify column SNAME char(30) ;

(iii)

Alter table STUDENT
Drop HOBBY ;

(iv)

Alter table STUDENT add column Path_wala char(30) ;