Note:
FORM_SUCCESS should not be used to test whether a COMMIT_FORM or POST built-in has succeeded.
Because COMMIT_FORM may cause many other triggers to fire, when you evaluate FORM_SUCCESS it may not reflect the status of COMMIT_FORM but of some other, more recently executed built-in.
A more accurate technique is to check that the SYSTEM.FORM_STATUS variable is set to 'QUERY' after the operation is done.
用form_success判断form是否没有错误，在某些时候是不能完全检测到form的错误。
比较正确的做法是对system.form_status是否是query进行判断。
IF Form_Success THEN
Commit;
IF :System.Form_Status <> 'QUERY' THEN
Message('Error prevented Commit');
RAISE Form_Trigger_Failure;
END IF;
END IF;
有时候看情况是否要增加SQLCODE的判断
IF form_success or SQLCODE = 0 THEN