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  A B
  id hyid hyid newid
  1 2 2 A
  2 3 3 B
  ÏÖÔÚÒª½«a±íµÄhyid»»³Éb±íµÄnewid,Çë×¢Òâa±íÖеÄhyid²»ÊÇΨһµÄ
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merge into a using b 
on (a.hyid=b.hyid)
when matched then
update set a.hyid=b.newid  
a.hyid ÔÚon¾äÖÐ,²»ÄÜÐÞ¸Ä

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²¢ÇÒÒòΪa±íÖеÄhyid²»ÊÇΨһµÄ,½á¹û´íÎóÎÞ·¨»ñµÃÎȶ¨ÐÐ

---

update a set hyid=(
  select newid from b where hyid=a.hyid)
where exists(
  select 1 from b where hyid=a.hyid)

---

SQL code:
update a set a.hyid=(select newid from b where b.hyid=a.hyid and rownum<2)
and exists (select 1 from b where b.hyid=a.hyid);

---

ÒýÓÃ

update a set hyid=(
select newid from b where hyid=a.hyid)
where exists(
select 1 from b where hyid=a.hyid)

1Â¥Õý½â£¬ÓÃmergeÎÞ·¨ÐÞ¸Ä

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---

--where rownum=1ÏÞÖÆÏÂ

update a set hyid=(
select newid from b where hyid=a.hyid where rownum=1)
where exists(
select 1 from b w