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select a ,max(b) as maxb from table group by a

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select a, max(b)
from tb
group by a

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select a ,max(b) as maxb from table group by a

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SQL code:
select a ,max(b) as maxb from table group by a

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ÒýÓà 1 Â¥ fardison µÄ»Ø¸´:
select a ,max(b) as maxb from table group by a


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SQL code:
with Table_A as (

select 'a1' a ,1 b from dual
union all
select 'a1' a ,2 b from dual
union all
select 'a1' a ,3 b from dual
union all
select 'a2' a ,1 b from dual
union all
select 'a2' a ,2 b from dual
union all
select 'a3' a ,1 b from dual
union all
select 'a4' a ,2 b from dual

)

SELECT *
from Table_A t1
WHERE EXISTS (SELECT t2.a, max(t2.b)
from Table_A t2
WHERE t2.a=t1.a
GROUP BY t2.a)