sql Óï¾ä

±íA
¿¨ºÅ         ʱ¼ä
1                 null
2                 null
3                 null
±íB
¿¨ºÅ       ʱ¼ä
1             2008-1-6
1             2004-5-3
2             2005-5-6
3             2003-5-9
3             2001-2-3

ÎÊÌ⣺¸üР  ±íAÀïµÄ   ÏàÓ¦¿¨ºÅµÄʱ¼äΪ   ±íBÀïÏàÓ¦¿¨ºÅµÄ£¨×îС£©Ê±¼ä
ÕýÈ·µÄ½á¹û£º
1       2004-5-3£¨×îС£©
2       2005-5-6
3       2001-2-3£¨×îС£©

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SQL code:
update a set
ʱ¼ä = b.ʱ¼ä
from tb1 as a
join tb2 as b
on a.¿¨ºÅ= b.¿¨ºÅ
where not exists(select * from tb2
where ¿¨ºÅ=b.¿¨ºÅ and ʱ¼ä> b.ʱ¼ä)

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SQL code:
update t set ʱ¼ä=(select min(ʱ¼ä) from tb where ¿¨ºÅ=t.¿¨ºÅ) from ta t

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SQL code

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