Question

我有许多客户的Microsoft SQL数据库，列是CustomerID,CustomerName,Locations,SQFT,EditDate, DateRecorded

每天，我们都会记录客户使用的面积。因此，数据库应该具有该月每天的值。我想为每位顾客选择面积最高的日子。以下代码仅返回单个客户，而不是所有客户。如何为每位客户返回当月最高的SQFT？

我的代码：

// $db_month_start = the first of the current month.
// $db_month_end = the end of the current month.
$query = "SELECT CustomerID,CustomerName,SQFT,EditDate 
          FROM SquareFootage 
          WHERE DateRecorded >= '{$db_month_start}' 
          AND DateRecorded <= '{$db_month_end}' 
          AND SQFT = (Select Max(SQFT) From SquareFootage WHERE DateRecorded >= '{$db_month_start}' AND DateRecorded <= '{$db_month_end}') ";

Answer 1

每位客户每月最高SQFT：

select  CustomerID
,       CustomerName
,       convert(varchar(7), DateRecorded, 120) as [Month]
,       max(SQFT) as MaxSQFTThisMonth
from    SquareFootage
group by
        CustomerID
,       CustomerName
,       convert(varchar(7), DateRecorded, 120)

这将适用于任意数月，并且多天内拥有最高SQFT的客户仅列在一行中。

Answer 2

您可以按照相同的路径进行操作。您只需要一个相关的子查询：

SELECT CustomerID, CustomerName, SQFT, EditDate 
FROM SquareFootage sf
WHERE DateRecorded >= '{$db_month_start}' AND DateRecorded <= '{$db_month_end}' AND
      SQFT = (Select Max(sf2.SQFT)
              From SquareFootage sf2
              WHERE sf2.DateRecorded >= '{$db_month_start}' AND
                    sf2.DateRecorded <= '{$db_month_end}' AND
                    sf2.CustomerId = sf.CustomerId
             );

Answer 3

with cte as (
   SELECT *, rank() over (partition by CustomerId order by SQFT desc) as [r]
   FROM SquareFootage 
   WHERE DateRecorded >= '{$db_month_start}' 
   AND DateRecorded <= '{$db_month_end}'
)
select CustomerID,CustomerName,SQFT,EditDate
from cte
where [r] = 1

此查询显示为“对于每个客户，按SQFT按相反顺序对记录进行排名。然后，返回每个客户的最高记录”。

从数据库中选择最高值，客户名称是唯一的？

3 个答案: