语法：

CREATE OR REPLACE TRIGGER trigger_name
INSTEAD OF operation    --delete,update,insert,create and so on
ON view_name
FOR EACH ROW
BEGIN
  ...
END;

hr@ORCL> CREATE TABLE A (ID NUMBER(5),COL VARCHAR2(5));

Table created.

hr@ORCL> CREATE TABLE B (ID NUMBER(5),COL VARCHAR2(5));

Table created.

hr@ORCL> CREATE OR REPLACE VIEW V_AB AS
  2      SELECT A.ID,A.COL AS COLA,B.COL AS COLB
  3       FROM A,B
  4      WHERE A.ID=B.ID
  5      /

View created.

hr@ORCL> CREATE OR REPLACE TRIGGER TRG_V_AB
  2      INSTEAD OF INSERT ON V_AB
  3      FOR EACH ROW
  4      BEGIN
  5      INSERT INTO A(ID,COL)VALUES(:NEW.ID,:NEW.COLA);
  6      INSERT INTO B(ID,COL)VALUES(:NEW.ID,:NEW.COLB);
  7      END;
  8      /

Trigger created.

hr@ORCL> SELECT TRIGGER_NAME,TRIGGER_TYPE FROM USER_TRIGGERS;

TRIGGER_NAME                   TRIGGER_TYPE
------------------------------ ----------------
TRG_V_AB                       INSTEAD OF

      
hr@ORCL> INSERT INTO V_AB VALUES(1,'AA','BB');

1 row created.

hr@ORCL> COMMIT;

Commit complete.

hr@ORCL> select * from a;

        ID COL
---------- -----
         1 AA

hr@ORCL> select * from b;

        ID COL
---------- -----
         1 BB

hr@ORCL> CREATE OR REPLACE VIEW  V_AB AS
  2      SELECT A.ID,B.COL AS COLA,A.COL AS COLB
  3       FROM A,B
  4      WHERE A.ID=B.ID
  5      /

View created.

hr@ORCL> INSERT INTO V_AB VALUES(1,'AA','BB');
INSERT INTO V_AB VALUES(1,'AA','BB')
*
ERROR at line 1:
ORA-01779: cannot modify a column which maps to a non key-preserved table


hr@ORCL> SELECT TRIGGER_NAME,TRIGGER_TYPE FROM USER_TRIGGERS;

no rows selected.