select domains - Firebird

select_domains_firebird.sql

SELECT
    RDB$FIELDS.RDB$FIELD_NAME
FROM
    RDB$FIELDS
    INNER JOIN RDB$RELATION_FIELDS
        ON (RDB$RELATION_FIELDS.RDB$FIELD_SOURCE = RDB$FIELDS.RDB$FIELD_NAME)
WHERE
    RDB$FIELDS.RDB$SYSTEM_FLAG = 0
GROUP BY
    RDB$FIELDS.RDB$FIELD_NAME

-- with the code below we have unused domains
HAVING
    COUNT(RDB$RELATION_FIELDS.RDB$FIELD_SOURCE) = 0

-- with the code below we have used domains
HAVING
    COUNT(RDB$RELATION_FIELDS.RDB$FIELD_SOURCE) > 0

Obs no unused alter left join