Booleans and UNKNOWN

TRUE and FALSE are concrete booleans. UNKNOWN represents a missing truth value. AND, OR, XOR and NOT propagate unknown according to three-valued logic.

RETURN NOT UNKNOWN AS unknown, FALSE AND UNKNOWN AS false_value,
       TRUE OR UNKNOWN AS true_value;

Truth predicates include IS [NOT] TRUE, IS [NOT] FALSE and IS [NOT] UNKNOWN. They test the truth category, rather than using ordinary equality with null.

RETURN UNKNOWN IS UNKNOWN AS unknown,
       UNKNOWN IS NOT FALSE AS not_false;

A truth predicate is a boolean, so it can be projected and deduplicated. Null is neither true nor false.

FOR n IN [TRUE, FALSE, UNKNOWN]
RETURN DISTINCT n IS TRUE AS truthy ORDER BY truthy;

WHERE and FILTER retain only true rows. A truth test of a property comparison classifies the result from each fragment’s stored type. An integer compared with those same digits stored as text is unknown, not true. Declared BOOLEAN session initializers also accept NOT UNKNOWN; the result is a null value subject to the declaration’s nullability constraint.