In MariaDB, FALSE is a synonym of 0 and TRUE is a synonym of 1. These
constants are case insensitive, so TRUE, True, and true are equivalent.

These terms are not synonyms of 0 and 1 when used with the IS operator. So,
for example, 10 IS TRUE returns 1, while 10 = TRUE returns 0 (because 1 != 10).

The IS operator accepts a third constant exists: UNKNOWN. It is always a
synonym of NULL.

TRUE and FALSE are reserved words, while UNKNOWN is not.

URL: https://mariadb.com/kb/en/sql-language-structure-boolean-literals/