Database-Management-System
August 29, 2024Database-Management-System
August 29, 2024Database-Management-System
| Question 654 |
In a relational database model, NULL values can be used for all but which one of the following ?
| To allow duplicate tuples in the table by filling the primary key column(s) with NULL. | |
| To avoid confusion with actual legitimate data values like 0 (zero) for integer columns and ’’ (the empty string) for string columns. | |
| To leave columns in a tuple marked as ’’unknown’’ when the actual value is unknown. | |
| To fill a column in a tuple when that column does not really ”exist” for that particular tuple. |
Question 654 Explanation:
→ NULL values are used in a relation when the value of column of a particular row is either Unknown or does Not Exist.
→ Sometimes the a column of a row does not contain any value or may have zero value in that case also NULL values are used to avoid any kind of confusion regarding the values of the column.
So, Option (B),(C) and (D) are the cases when NULL values are used in a relation.
Option(A) is incorrect because Primary key of a relation is a key which uniquely identify each tuple of a relation so it can’t have NULL values.
→ Sometimes the a column of a row does not contain any value or may have zero value in that case also NULL values are used to avoid any kind of confusion regarding the values of the column.
So, Option (B),(C) and (D) are the cases when NULL values are used in a relation.
Option(A) is incorrect because Primary key of a relation is a key which uniquely identify each tuple of a relation so it can’t have NULL values.
Correct Answer: A
Question 654 Explanation:
→ NULL values are used in a relation when the value of column of a particular row is either Unknown or does Not Exist.
→ Sometimes the a column of a row does not contain any value or may have zero value in that case also NULL values are used to avoid any kind of confusion regarding the values of the column.
So, Option (B),(C) and (D) are the cases when NULL values are used in a relation.
Option(A) is incorrect because Primary key of a relation is a key which uniquely identify each tuple of a relation so it can’t have NULL values.
→ Sometimes the a column of a row does not contain any value or may have zero value in that case also NULL values are used to avoid any kind of confusion regarding the values of the column.
So, Option (B),(C) and (D) are the cases when NULL values are used in a relation.
Option(A) is incorrect because Primary key of a relation is a key which uniquely identify each tuple of a relation so it can’t have NULL values.