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ID  Name  Calss Age
1  a    Ò»°à  12
2  b    Ò»°à  13
3  c    Ò»°à  10
4  d    ¶þ°à  12
5  e    ¶þ°à  11
6  f    ¶þ°à  18
7  g    Èý°à  19

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ID  Name  Calss Age
2  b    Ò»°à  13
6  f    ¶þ°à  18
7  g    Èý°à  19

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SQL code:
select * from tb t where age=(select max(age) from tb where name=t.name)

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SQL code:
--ÐÞ¸ÄÏÂ
select * from tb t where age=(select max(age) from tb where class=t.class)

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SQL code:
select * from tb t
where not exists(select * from tb where Calss=t.calss and age>t.age)

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SQL code:
-- =============================================
-- Author: T.O.P
-- Create date: 2009/12/01