oracle merge into on using 用法

MERGE INTO table1 a USING ( select id,name from table2) b ON (a.id=b.id)     
WHEN MATHED THEN update set a.name=b.name 
WHEN NOT MATHED THEN insert (id,name) values('id','name');

merge into 一般用于主键存在就更新其他字段，主键不存在就新增一条数据。
MATHED then后面的 update 不需要写表名，并且可以添加where条件，是对匹配到的结果集进行筛选。update 后面一般不用条件，其更新操作只对匹配到的结果集更新。

DECLARE 
       V_LANG CLOB := '超长字符串';
BEGIN
    merge into LM_BIDDING a
    using ( select NVL('甘肃省XXXXXXXXXX', '0' ) as title
    ,'TS00000063' as  custno
    ,NVL('2018-11-12', '0' ) as  releasedate
    ,NVL('甘肃省zz', '0' ) as purchaser  from dual) b
    on (NVL( a.TITLE, '0' )=b.title
    and a.CUSTNO=b.custno
    and NVL(  a.RELEASEDATE, '0' )=b.releasedate
    and  NVL(  a.PURCHASER, '0' )=b.purchaser )
    WHEN MATCHED THEN
      UPDATE SET AMDCNL=AMDCNL||'+1' --WHERE CUSTNO='TS00000063' AND RELEASEDATE='2018-11-12' AND TITLE='甘肃省XXXXXXXXXX' AND PURCHASER='甘肃省zz' 
    when not matched then insert ( BIDDINGID, CUSTNO, CREDITCODE, AGENCY, ANNODATE, ANNOITEM ) values ( 'Bxxxxx440', 'TS0xxxx063', '91620xxxx74835J', '甘肃xxxx有限公司', '2018-11-12', ' 服务/环境服务/空气污染治理服务') ; 
　　 
　　update LM_BIDDING set TEXT=TEXT||V_LANG where BIDDINGID = #{biddingid,jdbcType=VARCHAR} ;
　　　　
END;