獲取基於最新日期的最新數據 - MSSQL

Question

這是我的表怎麼看在我的數據庫： 我有2個表：

1. Location = ID, Name 
2. Product = ProdID, LocationID, CreatedDate 

------------------------------------------------- 
| ID   | Location  | CreatedDate  
------------------------------------------------- 
| 1234   | Location 1 | 2016-11-17 12:39 
| 4567   | Location 1 | 2016-11-17 12:39 
| 8978   | Location 1 | 2016-11-17 12:39  
| 8978   | Location 2 | 2016-11-17 13:39 
| 2578   | Location 1 | 2016-11-17 12:39 
| 1234   | Location 2 | 2016-11-18 12:39 
------------------------------------------------- 

我想檢索表象下面這樣：

---------------------------------------------- 
| Location 1 | Location 2 | Location 3 | 
---------------------------------------------- 
| 1234   | 1234   |    | 
| 4567   |    |    | 
| 8978   | 8978   | 8978   | 
| 2578   | 2578   | 2578   | 
---------------------------------------------- 

也是除上表我想查詢以獲得總量上的每個位置的最後一個掃描的唯一項目：

Location 1 count = 1 
Location 2 count = 1 
Location 3 count = 2 

說明：上表顯示了我們倉庫中不同物料的列表。 基本上，如果項目1234在位置1在12:00掃描並且在13:00掃描到位置2，則查詢只能從位置2獲取數據，因爲它是基於日期的最後一次更新。

Answer 1

顯然，您將進入內部連接，ID = LocationID。

除此之外，這是關於你的'where'子句。你需要子查詢來獲得每個項目的最大值（日期），我猜測它是你失蹤的部分。

Answer 2

你可以嘗試以下查詢

對於requirement1

select 
    case when Location1 = 0 then null else Location1 end Location1, 
    case when Location2 = 0 then null else Location2 end Location2, 
    case when Location3 = 0 then null else Location3 end Location3 
from(
    SELECT 
     SUM(case when location_id = 'Location 1' then id else 0 end) Location1, 
     SUM(case when location_id = 'Location 2' then id else 0 end) Location2, 
     SUM(case when location_id = 'Location 3' then id else 0 end) Location3 
    from Product 
    group by ProdID) t1; 

下面是上面的查詢

對於requirement2的結果，

select 
    sum(case when Location2 = 0 then 1 else 0 end) Location1, 
    sum(case when Location3 = 0 and Location2 <> 0 then 1 else 0 end) Location2, 
    sum(case when Location3 = 0 then 0 else 1 end) Location3 
from(
    SELECT 
     SUM(case when location_id = 'Location 1' then id else 0 end) Location1, 
     SUM(case when location_id = 'Location 2' then id else 0 end) Location2, 
     SUM(case when location_id = 'Location 3' then id else 0 end) Location3 
    from Product 
    group by id) t1; 

下面是上面的查詢

注的結果：如果是的ProdID整數上述查詢纔有效。

希望這可以幫助你。