從數據庫中選擇最高值，客戶名稱是唯一的？

Question

我有許多客戶的Microsoft SQL數據庫，列是CustomerID,CustomerName,Locations,SQFT,EditDate, DateRecorded

每天，我們都會記錄客戶使用的面積。 因此，數據庫應該具有該月每天的值。 我想為每位顧客選擇面積最高的日子。 以下代碼僅返回單個客戶，而不是所有客戶。 如何為每位客戶返回當月最高的SQFT？

我的代碼：

// $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

每位客戶每月最高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) 

這將適用於任意數月，並且具有多天最高SQFT的客戶僅列在一行中。

Answer 2

您可以按照相同的路徑進行操作。 你只需要一個相關的子查詢：

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

此查詢顯示為“對於每個客戶，按SQFT按相反順序對記錄進行排名。然后，返回每個客戶的最高記錄”。