求一个sql语句

id  number  sth      tosb
-------------------------------
1    20    XXX..      a
2    10    YYY..      a
3    13    ZZZ..      b
4    7    KKK..      b
5    19    PPP..      a

从表table里选择出对于同一个tosb，number最大的那个数据的sth，既

tosb    number      sth
-------------------------
a      20          XXX..
b      13          ZZZ..

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SQL code:
select *
from tb t
where
not exists(select 1 from tb where tosb=t.tosb and number>t.number)

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SQL code:
select * from tb
t where not eixsts(select 1 from tb where tosb=t.tosb and number>t.number)

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select
tosb  , number  ,    sth
from tb t
where not exists
(
select * from tb where t.tosb=tosb and t.number <number
)

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SQL code

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