Which operator checks for NULL values in a condition?

• A. IS NOT NULL
• B. = NULL
• C. <> NULL
• D. IS NULL

Answer: (D)

To check for missing values in SQL you use the IS NULL operator. NULL represents no value, and standard comparisons like = or <> don’t produce TRUE or FALSE when NULL is involved; they yield UNKNOWN, which means the condition won’t behave as you expect in a WHERE clause. Using IS NULL directly asks if a value is actually missing, and IS NOT NULL checks for the opposite. For example, a query like WHERE some_column IS NULL will return rows where that column has no value, while WHERE some_column IS NOT NULL returns rows where a real value exists.