选择每个组的最大值

Question

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

我的表看起来像这样.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

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

Answer 1

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

Answer 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

请注意,如果您有主键,这将更容易.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) 

Answer 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

Answer 4

select Name, Value, AnotherColumn
from out_pumptable
where Value =
(
  select Max(Value)
  from out_pumptable as f where f.Name=out_pumptable.Name
)
group by Name, Value, AnotherColumn

尝试这样，它有效。