在 SQL Server 中按最新日期获取 Distinct Id(FK)答案

【问题标题】：Getting Distinct Id(FK) by the latest date in SQL Server在 SQL Server 中按最新日期获取 Distinct Id(FK)
【发布时间】：2019-08-03 16:09:53
【问题描述】：

我目前正在处理一个查询，我需要根据创建的最新日期来区分 ID。

这是我的图表

|  ID  |    ModelID     |    LocationId   |  DateCreated  |
|------+----------------+-----------------+---------------|
|   1  |       1        |        5        |   02/03/2019  |
|   2  |       2        |      null       |   01/14/2019  |
|   3  |       2        |        0        |   02/03/2019  |
|   4  |       2        |        5        |   12/30/2018  |
|   5  |       4        |        3        |   01/10/2019  |
|   6  |       3        |        5        |   02/14/2019  |
|   7  |       2        |        5        |   03/13/2019  |

所以我的目标是区分ModelId，但仍然显示LocationId is null or equals to 0，如果LocationId 仍然相同，获取最新的DateCreated 并将其显示到列表中

期望的输出：

    |  ID  |    ModelID     |    LocationId   |  DateCreated  |
    +------+----------------+-----------------+---------------+
    |   1  |       1        |        5        |   02/03/2019  |
    |   2  |       2        |      null       |   01/14/2019  |<-still show
    |   3  |       2        |        0        |   02/03/2019  |<-still show
    |   4  |       2        |        5        |   03/13/2019  |<-The Latest
    |   5  |       4        |        3        |   01/10/2019  |
    |   6  |       3        |        5        |   02/14/2019  |

这是我当前的 SQL 查询：

SELECT 
    a.ModelID, a.LocationId,
    (SELECT TOP 1 
         CONVERT(NVARCHAR, DateCreated, 101) 
     FROM 
         db.DeliveryDates 
     WHERE
         isDeleted = 0 
         AND DeliveryId = a.DeliveryId) AS DateCreated,
FROM 
    db.DeliveryCarInfo a
WHERE
    a.isDeleted = 0

【问题讨论】：

标签： sql sql-server sql-server-2008 select distinct

【解决方案1】：

请尝试以下代码

DECLARE @DeliveryCarInfo TABLE (id int,modelId int,locationId int null,DateCreated date)

INSERT INTO @DeliveryCarInfo
(
    id,
    modelId,
    locationId,
    DateCreated
)
VALUES
(1  ,1 ,5,'02/03/2019'),
(2  ,2 ,null,'01/14/2019'), 
(3  ,2 ,0,'02/03/2019'),
(4  ,2 ,5,'12/30/2018'),
(5  ,4 ,3,'01/10/2019'),
(6  ,3 ,5,'02/14/2019'),
(7  ,2 ,5,'03/13/2019')

Select X.Id,X.modelId,X.locationId,X.DateCreated from (SELECT *,row_number() OVER (PARTITION by modelId,locationId ORDER BY dateCreated desc)R FROM @DeliveryCarInfo

)X
WHERE X.R=1

ORDER BY X.modelId,X.DateCreated

【讨论】：

谢谢先生，但它也会删除重复的modelId，即使它的null 和0 有两个值
了解，已更新我的查询，请使用更新后的代码
采纳为答案，非常感谢先生！这段代码已经卡了一天半了！真的是救命稻草

【解决方案2】：

请试试这个。

SELECT A.* from @tbl A
INNER JOIN
(
    SELECT ModelId,Max(DateCreated) As CreateDate from @tbl Group By ModelId
) As B
    ON B.ModelId = A.ModelId
    AND A.DateCreated = B.CreateDate

 UNION 

 Select * from @tbl A
 WHERE LocationId IS NULL OR LocationId = 0

【讨论】：

先生，我如何在您的代码中应用 db.DeliveryCarInfo 和 db.DeliveryDates 的表格。对不起
请替换此（来自）“SELECT ModelId,Max(DateCreated) As CreateDate from tbl Group By ModelId”替换为“SELECT ModelId,Max(DateCreated) As CreateDate from DeliveryCarInfo DCR INNER JOIN DeliveryDates DD ON DCR.Id =DCR.Id Group By DCR.ModelId”并将 tbl 替换为“DeliveryCarInfo”

【解决方案3】：

您可以尝试以下查询。联合将有助于获得预期的结果。

with cte
as 
(
SELECT a.ModelID 
        , a.LocationId 
        , (Select top 1 convert(nvarchar,DateCreated,101) from 
        db.DeliveryDates where isDeleted=0 and DeliveryId=a.DeliveryId) as 
         DateCreated
FROM db.DeliveryCarInfo a
WHERE a.isDeleted = 0
)
select ModelID, LocationId, DateCreated 
from cte 
where isnull(LocationId, 0) = 0

union

select ModelID, LocationId, max(DateCreated) as DateCreated
from cte
where isnull(LocationId, 0) != 0
group by ModelID, LocationId

【讨论】：

先生，我尝试了这个解决方案，但为什么我在 Group By 上获得了ModelID is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.？它
立即尝试更新查询。我无法验证，因为没有准备好表结构和数据。
为什么我的分组中的每一列都是我需要调用的，现在它正在寻找 DateCreated
再试一次...请与一些示例数据共享表结构，以便我可以运行查询并更正语法问题。您要选择的所有列都应该是分组依据或聚合函数的一部分。如果我们有（modelId 和 locationId）的唯一记录，那么我们不需要 group by 和 max 函数。正如我对位置 null 和 0 场景所假设的那样。

【解决方案4】：

您可以使用 ROW_NUMBER()

SELECT ModelID, LocationId, DateCreated FROM  (
    SELECT 
        a.ModelID, a.LocationId,
        CONVERT(NVARCHAR, d.DateCreated, 101) AS DateCreated,
        ROW_NUMBER() OVER(PARTITION BY a.ModelID, a.LocationId ORDER BY d.DateCreated DESC) RN
    FROM 
        db.DeliveryCarInfo a
            LEFT JOIN db.DeliveryDates d ON d.DeliveryId = a.DeliveryId AND d.isDeleted = 0 
    WHERE
        a.isDeleted = 0
) AS T WHERE RN = 1

【讨论】：