触发器中的after与before理解

做一个表的insert的trigger，目的是只修改插入行的字段。  

CREATE OR REPLACE TRIGGER TR_RME_SLOT 
BEFORE  INSERT ON RME_SLOT 
FOR EACH ROW 
BEGIN 
  IF (:NEW.POSITION >= 0 AND :NEW.POSITION <10) THEN 
      :NEW.SLOT_NAME := '0'||TO_CHAR(:NEW.POSITION); 
  ELSE 
      :NEW.SLOT_NAME := TO_CHAR(:NEW.POSITION); 
  END IF; 
END;  

在插入以前就需要修改插入行；在trigger实现中并不需要用到update语句  

同时，如果要在trigger中实现对本表记录的修改，则需要这样写：  

CREATE OR REPLACE TRIGGER TR_RME_SLOT 
AFTER  INSERT ON RME_SLOT 
FOR EACH ROW 
DECLARE 
   PRAGMA AUTONOMOUS_TRANSACTION; 
BEGIN 
  IF (:NEW.POSITION >= 0 AND :NEW.POSITION <10) THEN 
      UPDATE RME_SLOT  SET SLOT_NAME = '0'||TO_CHAR(:NEW.POSITION) WHERE SLOT_ID=:NEW.SLOT_ID; 
  ELSE 
      UPDATE RME_SLOT  SET SLOT_NAME = TO_CHAR(:NEW.POSITION) WHERE SLOT_ID=:NEW.SLOT_ID; 
  END IF; 
  COMMIT; 
END; 

注意多了一段DECLARE，同时在trigger结束时需要COMMIT

CREATE OR REPLACE TRIGGER tr_AfterUpdate
AFTER INSERT OR UPDATE
ON TEST_TRIGGER
FOR EACH ROW
DECLARE
PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN

   UPDATE TEST_TRIGGER
   SET T_FACT = T_SALARY*(1-T_TAX)-T_EAT-T_HOUSE
   WHERE T_NAME = :NEW.T_NAME;
   COMMIT;  

   EXCEPTION
     WHEN OTHERS THEN
       -- Consider logging the error and then re-raise
       RAISE;
END tr_testUpdate;