oracle如何把update(含max函数的语句)改为merge into呢

create table DATA_MODEL_FINAL
(
  OBJID           NUMBER not null,
  OBJUSERID       VARCHAR2(20),
  OBJELEVATION    FLOAT,
  GROUPID         VARCHAR2(20) default 0
);
create bitmap index GROUPID_model_index on data_model_final(GROUPID);
create unique index objuserid_index on data_model_final(objuserid);
  create table DATA_PIPE_FINAL
(
  OBJID              NUMBER not null,
  STARPOINTELEVATION FLOAT,
  GROUPID            VARCHAR2(20) default 0,
  START_POINT        VARCHAR2(20)

);
create index START_POINT_index on data_pipe_final(START_POINT);
create bitmap index GROUPID_pipe_index on data_pipe_final(GROUPID);

insert into DATA_MODEL_FINAL (OBJID,OBJUSERID,OBJELEVATION,GROUPID) values (1910615,'AJ31123',0,'0201');
insert into DATA_MODEL_FINAL (OBJID,OBJUSERID,OBJELEVATION,GROUPID) values (1910616,'AJ31124',0,'0202');
insert into DATA_MODEL_FINAL (OBJID,OBJUSERID,OBJELEVATION,GROUPID) values (1910617,'AJ31125',0,'0203');
insert into DATA_MODEL_FINAL (OBJID,OBJUSERID,OBJELEVATION,GROUPID) values (1910618,'AJ31126',0,'0204');
insert into DATA_MODEL_FINAL (OBJID,OBJUSERID,OBJELEVATION,GROUPID) values (1910619,'AJ31127',0,'0204');
insert into DATA_MODEL_FINAL (OBJID,OBJUSERID,OBJELEVATION,GROUPID) values (1910620,'AJ31128',0,'0204');


insert into data_pipe_final (OBJID,START_POINT,STARPOINTELEVATION,GROUPID) values (201101,'AJ31126',1.5,'0104');
insert into data_pipe_final (OBJID,START_POINT,STARPOINTELEVATION,GROUPID) values (201102,'B000001',1.8,'0101');
insert into data_pipe_final (OBJID,START_POINT,STARPOINTELEVATION,GROUPID) values (201103,'AJ31126',2.2,'0104');
insert into data_pipe_final (OBJID,START_POINT,STARPOINTELEVATION,GROUPID) values (201104,'AJ31126',1.5,'0104');
insert into data_pipe_final (OBJID,START_POINT,STARPOINTELEVATION,GROUPID) values (201105,'AJ31127',1.5,'0104');
insert into data_pipe_final (OBJID,START_POINT,STARPOINTELEVATION,GROUPID) values (201106,'AJ31127',1.9,'0104');

        UPDATE DATA_MODEL_FINAL A SET OBJELEVATION=(SELECT MAX(B.STARPOINTELEVATION) FROM DATA_PIPE_FINAL B
           WHERE B.GROUPID='0104' AND B.START_POINT=A.OBJUSERID
           ) WHERE A.GROUPID='0204';

    merge into DATA_MODEL_FINAL A     
    using DATA_PIPE_FINAL B       
    on (B.GROUPID='0104' AND A.GROUPID='0204' AND B.START_POINT=A.OBJUSERID)        
    when matched then      
    update set A.OBJELEVATION=MAX(B.STARPOINTELEVATION)

 merge into DATA_MODEL_FINAL A     
    using (SELECT MAX(STARPOINTELEVATION) as STARPOINTELEVATION, START_POINT FROM DATA_PIPE_FINAL
               WHERE GROUPID='0104'    
            group by START_POINT) b
    on (A.GROUPID='0204' AND B.START_POINT=A.OBJUSERID)        
    when matched then      
    update set A.OBJELEVATION=MAX(B.STARPOINTELEVATION)