treasuredb/schema/triggers/enforceFixedCredit.sql

CREATE TRIGGER enforceFixedCredit
    BEFORE UPDATE OF account, value ON Credit
    WHEN EXISTS (SELECT * FROM Transfer WHERE credId=NEW.credId)
     AND NOT EXISTS (SELECT * FROM __INTERNAL_TRIGGER_STACK)
BEGIN
    SELECT RAISE(FAIL, "Credit involved in transactions to revoke at first");
END;