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select c,d from a group by c

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select  *  from  a  where  not  exists(select  1  from  a  b  where  name=b.c  and  d>b.d)

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select * from a where c not in (select c from a group by c having count(c)>1)

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SQL code:
select *
from a t
where (select count(1) from tb where c=t.c)=1

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SQL codeselect*from a twhere (selectcount(1)from tbwhere c=t.c)=1

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SQL code:
select *
from a t
where (select count(1) from a where c=t.c)=1

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select *
from A
group by c