SQL operator that returns true when the value is NULL and false otherwise

• A. Is Null
• B. Is Not Null
• C. Equals
• D. Like

Answer: (A)

In SQL, NULL represents missing or unknown data, and comparisons with NULL follow three-valued logic: TRUE, FALSE, or UNKNOWN. The operator IS NULL evaluates to TRUE when the value is NULL and to FALSE otherwise, making it the correct way to test for the absence of a value. Using equality won't work because NULL = NULL yields UNKNOWN, not TRUE, so it won’t satisfy a WHERE clause as a true condition. Other predicates like LIKE or normal equality are not true for NULL values; they return UNKNOWN for NULL, which is treated as false in filters. Therefore, the expression that returns true exactly when a value is NULL is IS NULL.