关于oracle数据库的问题，帮忙看看哪错了。。。
merge into hy_wldw a
using (select * from jh_jk_order where TRANSID in('646','645')) b
on (a.dwno =b.SELLERID)
when matched then
  update
  set a.dwmc = b.sname,
  a.dwlx = '2',
  a.dz = b.saddress,
  a.cs = decode(b.FROMDISTRICT, null, b.FROMCITY, b.FROMDISTRICT),
  a.sf = b.FROMPROV,
  a.lxr = b.sname,
  a.dh = b.SMOBILEPHONE,
  a.sjno = b.SELLERID,
  a.yzbm = '1',
  a.xtfl = '1'
when not matched then
  insert
  ( dwmc, dwlx, dz, cs, sf, lxr, dh, sjno, yzbm, xtfl)
  values
  (
  b.SNAME,
  '2',
  b.SADDRESS,
  decode(b.FROMDISTRICT, null, b.FROMCITY, b.FROMDISTRICT),
  b.FROMPROV,
  b.SNAME,
  b.SMOBILEPHONE,
  b.SELLERID,
  '1',
  '1')


------解决方案--------------------
肯定有某个空值约束，这个要好好看看自己的，也有可能是jh_jk_order表出來的值是NULL导致
------解决方案--------------------
肯定应该有不允许为空的字段吧，否则如果都为空还有什么意义。