SQL - 查詢報告MAX DATE結果或NULL結果

Question

我有3代表的SQL數據庫：

1. Customer record表，持主數據（每行是唯一的）
2. Customer notes，每個音符數據/時間戳記（有可能是每個客戶的音符，或根本沒有）

3. Product表，顯示該客戶已經購買該產品

   表：tbl_Customer_記錄
   客戶ID ----公司名稱公司----- -----段促銷代碼

   表：tbl_Customer_Notes
   客戶ID ----注意-----創建日期

   表：tbl_Customer_Products
   客戶ID ----產品類別

我想就是拉僅包含最新備註的客戶記錄列表，因此如果存在多個備註，則不存在重複行。但我也希望我的報告包含客戶記錄，如果根本沒有記錄。我已經用SELECT MAX函數實現了第一部分，並且運行良好，問題是當我在下面的最後一行代碼中添加OR = NULL子句時。這是行不通的，我找不出解決方案。

任何建議將不勝感激！

SELECT   

[tbl_Customer_Records].[CustomerID], 
[tbl_Customer_Records].[Company Name], 
[tbl_Customer_Records].[Company Segment], 
[tbl_Customer_Records].[Promo Code], 
[tbl_Customer_Notes].[Note], 
[tbl_Customer_Products].[Product Category] 

FROM    

tbl_Customer_Records 
LEFT OUTER JOIN tbl_Customer_Notes 
ON tbl_Customer_Records.CustomerID = tbl_Customer_Notes.CustomerID 
LEFT OUTER JOIN tbl_Customer_Products 
ON tbl_Customer_Records.CustomerID = tbl_Customer_Products.CustomerID 

WHERE 
[Product Category] in ('Nuts','Bolts','Screws','Spanners') 

AND 

[Created Date] in (SELECT MAX ([Created Date]) FROM tbl.Customer_Notes GROUP BY [CustomerID]) 

OR tbl_Customer_Note.Note is null 

Answer 1

是有一些技巧做這樣的查詢（ROW_NUMBER或分組數據連接），但我認爲最乾淨的一個了你的情況是使用外部應用：

select 
    cr.[CustomerID], 
    cr.[Company Name], 
    cr.[Company Segment], 
    cr.[Promo Code], 
    cn.[Note], 
    cp.[Product Category] 
from tbl_Customer_Records as cr 
    left outer join tbl_Customer_Products as cp on cp.CustomerID = cr.CustomerID 
    outer apply (
     select top 1 
      t.[Note] 
     from tbl_Customer_Notes as t 
     where t.[CustomerID] = cr.[CustomerID] 
     order by t.[Created_Date] desc 
    ) as cn 
where 
    cp.[Product Category] in ('Nuts','Bolts','Screws','Spanners') 

改變了所有笨拙table name.column name到alias.column name，我認爲這是更具可讀性這種方式。

或者：

select 
    cr.[CustomerID], 
    cr.[Company Name], 
    cr.[Company Segment], 
    cr.[Promo Code], 
    cn.[Note], 
    cp.[Product Category] 
from tbl_Customer_Records as cr 
    left outer join tbl_Customer_Products as cp on cp.CustomerID = cr.CustomerID 
    left outer join tbl_Customer_Notes as cn on 
     cn.CustomerID = cr.CustomerID and 
     cn.[Created_Date] = (select max(t.[Created_Date]) from tbl_Customer_Notes as t where t.CustomerID = cr.CustomerID) 
where 
    cp.[Product Category] in ('Nuts','Bolts','Screws','Spanners') 

Answer 2

嘗試使用CustomerID not in (select CustomerID from tbl_Customer_Note)

Answer 3

可以在ON謂詞添加您的篩選條件，從左邊的表保存行，只獲取需要從右表的匹配行，從第一LEFT OUTER JOIN操作。下面的查詢應該工作：

SELECT   
CR.[CustomerID], 
CR.[Company_Name], 
CR.[Company_Segment], 
CR.[Promo_Code], 
CN.[Note], 
CP.[Product_Category] 
FROM    
tbl_Customer_Records CR 
LEFT OUTER JOIN tbl_Customer_Notes CN 
ON CR.CustomerID = CN.CustomerID AND CN.[Created_Date] in (SELECT MAX ([Created_Date]) 
                  FROM tbl_Customer_Notes 
                  WHERE CR.CustomerID = tbl_Customer_Notes.CustomerID 
                  GROUP BY [CustomerID]) 
LEFT OUTER JOIN tbl_Customer_Products CP 
ON CR.CustomerID = CP.CustomerID 
WHERE 
[Product_Category] in ('Nuts','Bolts','Screws','Spanners') 

Answer 4

應該工作，試圖用NULL值：

SELECT a.[CustomerID], 
     a.[Company Name], 
     a.[Company Segment], 
     a.[Promo Code], 
     a.[Note], 
     a.[Product Category] 
FROM (
SELECT   
cr.[CustomerID], 
cr.[Company Name], 
cr.[Company Segment], 
cr.[Promo Code], 
cn.[Note], 
cp.[Product Category], 
ROW_NUMBER() OVER(PARTITION BY cr.[CustomerID] ORDER BY cn.[Created Date] DESC) as rnk 
FROM tbl_Customer_Records cr 
LEFT JOIN tbl_Customer_Notes cn 
ON cr.CustomerID = cn.CustomerID 
LEFT JOIN tbl_Customer_Products cp 
ON cr.CustomerID = cp.CustomerID 
WHERE cp.[Product Category] in ('Nuts','Bolts','Screws','Spanners'))a 
WHERE a.rnk = 1