ORACLE插入失败后更新

create table t1(cid int,cname varchar2(100));
insert into t1 values (1,'1');
create table t2(cid int,cname varchar2(100));
insert into t2 values(1,'3');       
insert into t2 values(2,'4'); 

MERGE INTO t1 a
      USING t2 b
    on (a.cid=b.cid)
    WHEN MATCHED  THEN
        UPDATE SET a.cname=b.cname
    WHEN NOT MATCHED THEN
        INSERT (a.cid,a.cname ) VALUES ( b.cid,b.cname );