Pasted

SELECT
   S.RDB$FIELD_NAME
FROM RDB$INDEX_SEGMENTS S
LEFT JOIN RDB$RELATION_CONSTRAINTS RC ON (RC.RDB$INDEX_NAME = S.RDB$INDEX_NAME)
WHERE
   RC.RDB$RELATION_NAME = 'PESSOA' -- Coloque aqui o nome da tabela
   AND RC.RDB$CONSTRAINT_TYPE = 'PRIMARY KEY'