选择每个组的最大值

Name    Value   AnotherColumn
-----------
Pump 1  8000.0  Something1
Pump 1  10000.0 Something2
Pump 1  10000.0 Something3
Pump 2  3043    Something4
Pump 2  4594    Something5
Pump 2  6165    Something6

My table looks something like this. I would like to know how to select max value for each pump.

我的桌子是这样的。我想知道如何为每个泵选择最大值。

select a.name, value from out_pumptable as a,
(select name, max(value) as value from out_pumptable where group by posnumber)g where and g.value = value

this code does the job, but i get two entries of Pump 1 since it has two entries with same value.

这段代码完成了这项工作，但是我得到了泵1的两个条目，因为它有两个具有相同值的条目。

4 个解决方案

#1

select name, max(value)
from out_pumptable
group by name

#2

SELECT
  b.name,
  MAX(b.value) as MaxValue,
  MAX(b.Anothercolumn) as AnotherColumn
FROM out_pumptabl
INNER JOIN (SELECT 
              name,
              MAX(value) as MaxValue
            FROM out_pumptabl
            GROUP BY Name) a ON 
  a.name = b.name AND a.maxValue = b.value
GROUP BY b.Name

Note this would be far easier if you had a primary key. Here is an Example

注意，如果您有一个主键，这将容易得多。这是一个例子

SELECT * FROM out_pumptabl c
WHERE PK in 
    (SELECT
      MAX(PK) as MaxPK
    FROM out_pumptabl b
    INNER JOIN (SELECT 
                  name,
                  MAX(value) as MaxValue
                FROM out_pumptabl
                GROUP BY Name) a ON 
      a.name = b.name AND a.maxValue = b.value) 

#3

select name, value 
from( select name, value, ROW_NUMBER() OVER(PARTITION BY name ORDER BY value desc) as rn
from out_pumptable ) as a
where rn = 1

#4

SELECT DISTINCT (t1.ProdId), t1.Quantity FROM Dummy t1 INNER JOIN
       (SELECT ProdId, MAX(Quantity) as MaxQuantity FROM Dummy GROUP BY ProdId) t2
    ON t1.ProdId = t2.ProdId
   AND t1.Quantity = t2.MaxQuantity
 ORDER BY t1.ProdId

this will give you the idea.

这将给你一个想法。