Which concept defines the three boolean values SQL uses: TRUE, FALSE, and UNKNOWN?

• A. Boolean logic
• B. Three valued logic (3vl)
• C. Fuzzy logic
• D. Binary logic

Answer: (B)

Three-valued logic is used in SQL to account for NULL, which represents unknown or missing data. In SQL, comparisons involving NULL don’t yield TRUE or FALSE; they yield UNKNOWN. Logical operators like AND and OR are defined to handle UNKNOWN in a consistent way, so queries can reason about conditions even when some values are unknown. This framework, with TRUE, FALSE, and UNKNOWN as the possible truth values and specific operator rules for combining them, best describes how SQL evaluates conditions.

Boolean or binary logic would only have TRUE and FALSE and can’t model UNKNOWN. Fuzzy logic uses degrees of truth between 0 and 1, not a separate UNKNOWN state, so it doesn’t fit SQL’s NULL semantics.