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Boolean Logic

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    Some clauses, such as WHERE, WHEN, and HAVING, require values to be interpreted as Boolean values.

    The following rules apply when evaluating these types of clauses:

    • MISSING, NULL, and FALSE are FALSE

    • numbers +0, -0, and NaN are FALSE

    • empty strings, arrays, and objects are FALSE

    • all other values are TRUE

    Four-valued logic

    In SQL++, Boolean propositions can evaluate to NULL or MISSING (as well as to TRUE and FALSE).

    The following table describes how these values relate to the logical operators:

    a b a AND b a OR b NOT a

    TRUE

    TRUE

    TRUE

    TRUE

    FALSE

    FALSE

    FALSE

    TRUE

    NULL

    NULL

    TRUE

    MISSING

    MISSING

    TRUE

    FALSE

    TRUE

    FALSE

    TRUE

    TRUE

    FALSE

    FALSE

    FALSE

    NULL

    FALSE

    NULL

    MISSING

    FALSE

    MISSING

    NULL

    TRUE

    NULL

    TRUE

    NULL

    FALSE

    FALSE

    NULL

    NULL

    NULL

    NULL

    MISSING

    MISSING

    NULL

    MISSING

    TRUE

    MISSING

    TRUE

    MISSING

    FALSE

    FALSE

    MISSING

    NULL

    MISSING

    NULL

    MISSING

    MISSING

    MISSING

    Comparing NULL and MISSING values

    Operator Non-NULL Value NULL MISSING

    IS NULL

    FALSE

    TRUE

    MISSING

    IS NOT NULL

    TRUE

    FALSE

    MISSING

    IS MISSING

    FALSE

    FALSE

    TRUE

    IS NOT MISSING

    TRUE

    TRUE

    FALSE

    IS VALUED

    TRUE

    FALSE

    FALSE

    IS NOT VALUED

    FALSE

    TRUE

    TRUE