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प्रश्न
Explain the concept of “Alternate Key” in a Relational Database Management System with an appropriate example.
उत्तर
Alternate keys refer to all candidate keys that are not primary keys.
Example: Consider the table student as per the following structure:
| Table: Student | ||||
| Roll | Name | Phone | Aadhar | Marks |
In the student table:
Candidate keys: Roll, Phone, Aadhar
If the Primary key is: Roll
Alternate keys: Aadhar, Phone
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संबंधित प्रश्न
Minimal superkeys are known as?
The attributes which have all the properties of primary key
The primary key can be?
______ refers to the attribute that can uniquely identify tuples within the relation.
An Alternate key can be defined as ______.
Attributes that are candidates for primary keys are called ______.
An attribute in a table whose value is derived from primary key of another table is known as ______.
Which of the following is true for a tuple and attribute?
Why foreign keys are allowed to have NULL values? Explain with an example.
Differentiate between Primary key and foreign key.
In a multiplex, movies are screened in different auditoriums. One movie can be shown in more than one auditorium. In order to maintain the record of movies, the multiplex maintains a relational database consisting of two relations viz. MOVIE and AUDI respectively as shown below:
Movie(Movie_ID, MovieName, ReleaseDate) Audi(AudiNo, Movie_ID, Seats, ScreenType, TicketPrice)
Is it correct to assign Movie_ID as the primary key in the MOVIE relation? If no, then suggest an appropriate primary key.
In a multiplex, movies are screened in different auditoriums. One movie can be shown in more than one auditorium. In order to maintain the record of movies, the multiplex maintains a relational database consisting of two relations viz. MOVIE and AUDI respectively as shown below:
Movie(Movie_ID, MovieName, ReleaseDate) Audi(AudiNo, Movie_ID, Seats, ScreenType, TicketPrice)
Is it correct to assign AudiNo as the primary key in the AUDI relation? If no, then suggest an appropriate primary key.
| Student Project Database | ||||
| Table: STUDENT | ||||
| Roll No | Name | Class | Section | Registration_ID |
| 11 | Mohan | XI | 1 | IP-101-15 |
| 12 | Sohan | XI | 2 | IP-104-15 |
| 21 | John | XII | 1 | CS-103-14 |
| 22 | Meena | XII | 2 | CS-101-14 |
| 23 | Juhi | XII | 2 | CS-101-10 |
| Table: PROJECT | ||||
| ProjectNo | PName | SubmissionDate | ||
| 101 | Airline Database | 12/01/2018 | ||
| 102 | Library Database | 12/01/2018 | ||
| 103 | Employee Database | 15/01/2018 | ||
| 104 | Student Database | 12/01/2018 | ||
| 105 | Inventory Database | 15/01/2018 | ||
| 106 | Railway Database | 15/01/2018 | ||
| PROJECT ASSIGNED | ||||
| Registration_ID | ProjectNo | |||
| IP-101-15 | 101 | |||
| IP-104-15 | 103 | |||
| CS-103-14 | 102 | |||
| CS-101-14 | 105 | |||
| CS-101-10 | 104 | |||
- Name the primary key of each table.
- Find foreign key(s) in table PROJECT-ASSIGNED.
- Is there any alternate key in table STUDENT? Give justification for your answer.
- Can a user assign duplicate value to the field RollNo of STUDENT table? Justify.
| Student Project Database | ||||
| Table: STUDENT | ||||
| Roll No | Name | Class | Section | Registration_ID |
| 11 | Mohan | XI | 1 | IP-101-15 |
| 12 | Sohan | XI | 2 | IP-104-15 |
| 21 | John | XII | 1 | CS-103-14 |
| 22 | Meena | XII | 2 | CS-101-14 |
| 23 | Juhi | XII | 2 | CS-101-10 |
| Table: PROJECT | ||||
| ProjectNo | PName | SubmissionDate | ||
| 101 | Airline Database | 12/01/2018 | ||
| 102 | Library Database | 12/01/2018 | ||
| 103 | Employee Database | 15/01/2018 | ||
| 104 | Student Database | 12/01/2018 | ||
| 105 | Inventory Database | 15/01/2018 | ||
| 106 | Railway Database | 15/01/2018 | ||
| PROJECT ASSIGNED | ||||
| Registration_ID | ProjectNo | |||
| IP-101-15 | 101 | |||
| IP-104-15 | 103 | |||
| CS-103-14 | 102 | |||
| CS-101-14 | 105 | |||
| CS-101-10 | 104 | |||
For the above-given database STUDENT-PROJECT, can we perform the following operations?
- Insert a student record with a missing roll number value.
- Insert a student record with a missing registration number value.
- Insert a project detail without a submission date.
- Insert a record with registration ID IP-101-19 and ProjectNo 206 in the table PROJECT-ASSIGNED.
| Student Project Database | ||||
| Table: STUDENT | ||||
| Roll No | Name | Class | Section | Registration_ID |
| 11 | Mohan | XI | 1 | IP-101-15 |
| 12 | Sohan | XI | 2 | IP-104-15 |
| 21 | John | XII | 1 | CS-103-14 |
| 22 | Meena | XII | 2 | CS-101-14 |
| 23 | Juhi | XII | 2 | CS-101-10 |
| Table: PROJECT | ||||
| ProjectNo | PName | SubmissionDate | ||
| 101 | Airline Database | 12/01/2018 | ||
| 102 | Library Database | 12/01/2018 | ||
| 103 | Employee Database | 15/01/2018 | ||
| 104 | Student Database | 12/01/2018 | ||
| 105 | Inventory Database | 15/01/2018 | ||
| 106 | Railway Database | 15/01/2018 | ||
| PROJECT ASSIGNED | ||||
| Registration_ID | ProjectNo | |||
| IP-101-15 | 101 | |||
| IP-104-15 | 103 | |||
| CS-103-14 | 102 | |||
| CS-101-14 | 105 | |||
| CS-101-10 | 104 | |||
For the above-given database STUDENT-PROJECT, can we perform the following operation?
Insert a student record with a missing registration number value.
Explain the use of ‘Foreign Key’ in a Relational Database Management System. Give example to support your answer.
Which of the following statements is FALSE about keys in a relational database?
Give one difference between alternate key and candidate key.
