Question

If the value of an attribute in a tuple is not known or not applicable or not available, a special value called ................ is used to represent them.

• A. EMPTY
• B. BLANK
• C. NULL
• D. VOID

Hint:

Use NULL in databases to represent unknown or inapplicable values — it means "value is missing."

Answer 1

The Correct Option is C

In relational databases, when the value of a specific field or attribute is unknown, undefined, or inapplicable, it is represented using the special marker NULL.
NULL is not the same as zero, empty string, or blank — it signifies the complete absence of a value.
This helps maintain the integrity of database operations by clearly distinguishing unknown or missing data from actual values.
SQL queries must handle NULL values carefully, as standard operators behave differently when NULL is involved.
For instance, comparison with NULL using equality will not return true — instead, IS NULL or IS NOT NULL should be used.
Thus, NULL serves as a placeholder for unknown or missing data in database systems.