oracle判断时间字段格式函数，并触发器转换格式

CREATE OR REPLACE FUNCTION isdate(datestr VARCHAR2)
RETURN INT
IS
p_date   DATE;
BEGIN
SELECT TO_DATE (datestr, 'YYYY-MM-DD HH24:MI:SS')
INTO p_date
FROM DUAL;

RETURN 1;
EXCEPTION
WHEN OTHERS
THEN
RETURN 0;
END;

create or replace trigger transferTime
after insert on was_flow_log
for each row
  declare
  pragma autonomous_transaction;
  begin
    UPDATE was_flow_log t set t.log_when = TO_CHAR(t.log_when/(1000 * 60 * 60 * 24) + TO_DATE('1970-01-01 08:00:00', 'YYYY-MM-DD HH24:MI:SS'),'YYYY-MM-DD HH24:MI:SS') where ISDATE(t.log_when)='0';
    UPDATE was_flow_log t set t.promisetime = TO_CHAR(t.promisetime/(1000 * 60 * 60 * 24) + TO_DATE('1970-01-01 08:00:00', 'YYYY-MM-DD HH24:MI:SS'),'YYYY-MM-DD HH24:MI:SS') where ISDATE(t.promisetime)='0';

    commit;
end;