sql - 如何在 Oracle 中创建计算派生值的触发器

Question

当在 ContractInfo 中插入元组时，创建一个触发器来计算持续时间列的值。

ContractInfo Table
HAS_CONTRACT          DATE_FROM DATE_TO     DURATION
--------------------- --------- --------- ----------
Simon Palm            20-AUG-01 19-AUG-02          0
Simon Palm            20-SEP-02 19-AUG-03          0
Flut                  10-JUN-99 09-SEP-02          0

我怎样才能触发？我对触发器有点困惑。

Answer 1

SQL> create or replace trigger ContractInfo_buifer
  2  before insert or update on contractinfo
  3  for each row
  4  declare
  5  begin
  6    :new.duration := :new.date_to - :new.date_from; -- answer in days.
  7  END;
  8  /

Trigger created.

SQL> insert into ContractInfo (HAS_CONTRACT,  DATE_FROM, DATE_TO ) values ('Simon Palm', to_date('20-AUG-01', 'dd-mon-rr'), to_date('19-AUG-02', 'dd-mon-rr'))
  2  /

1 row created.

SQL> select * from contractinfo;

HAS_CONTRA DATE_FROM DATE_TO     DURATION
---------- --------- --------- ----------
Simon Palm 20-AUG-01 19-AUG-02        364

Answer 2

这就是我对 Oracle 的处理方式：

CREATE OR REPLACE TRIGGER TRIG_ContractInfo
    BEFORE INSERT OR UPDATE ON ContractInfo REFERENCING
    NEW AS NEW
    OLD AS OLD
    FOR EACH ROW
DECLARE
BEGIN
  IF INSERTING THEN
    /* ON INSERT STATEMENTS */
  END IF;
  IF UPDATING THEN
    /* ON UPDATE STATEMENTS */
  END IF;
  /* COMMON STATEMENTS */
END;
/