Boolean data type

The Boolean data type represents the values of true, false, and unknown.

Boolean constants TRUE, FALSE, and UNKNOWN represent the corresponding Boolean truth values. ON and OFF are synonyms for TRUE and FALSE. UNKNOWN is identical to the NULL constant.

When performing comparisons and assignments, a Boolean value is compatible with character and graphic strings, and numeric values that are integer or decimal floating point values. String values representing true are 't' , 'true' , 'y', 'yes' , 'on', and '1'. False can be represented by 'f', 'false', 'n', 'no', 'off', and '0'. Any combination of uppercase and lowercase characters are recognized. Numeric values are interpreted as false if they have a value of 0. Otherwise, they are true.

The normal comparison predicates can be used with Boolean values. A Boolean predicate of IS TRUE or IS FALSE can be used as well. In addition, a Boolean value can be specified alone in a predicate, which is an implicit use of the IS TRUE predicate. For comparisons, true is greater than false.

The following three predicates have the same meaning:

... WHERE SHIPPED = TRUE

... WHERE SHIPPED IS TRUE

... WHERE SHIPPED

Altering a column between any other data type and Boolean is not supported.