根据sql查询中的条件查找值对

Question

我有样本查询 SQL Fiddle。我需要找到对值（a，1），（c，2），因为对于它们列 SomeCount 具有最高值。谢谢 ; ）

Answer 1

select SomeName, SerialNo
from testTable
group by SerialNo -- because you want to have the biggest result of SomeCount from a set of rows with the same SerialNo
order by SomeCount DESC -- because you want to have the result with the biggest SomeCount

Answer 2

使用联接获取分组最大行的两种方法我假设SerialNo为一组

方法1

使用左连接

select concat(t.SomeName,',',t.SerialNo) pair
,t.*
from testTable t
left join testTable t1 
     on(t.SerialNo = t1.SerialNo
        and t.SomeCount < t1.SomeCount)
WHERE t1.SerialNo IS NULL;

方法2

使用内部联接和子选择

select concat(t.SomeName,',',t.SerialNo) pair
,t.*
from testTable t
join (select SerialNo ,max(SomeCount) SomeCount 
      from testTable
     group by SerialNo) t1 
on(t.SerialNo = t1.SerialNo  and t.SomeCount = t1.SomeCount)

Fiddle demo

Group-wise Maximum of a Certain Column