基于另一列的最大值的列上的SQL内连接

Question

我有两个表,一个"主"是主列表的名称,第二个"方案"是主列表中每个名称的多个方案的列表.我希望我的INNER JOIN查询从"scenario"表中获取具有列状态的ID的主列表,但仅获取基于scenarioID的最新状态.这是我尝试的代码和具有所需输出的表

SELECT DISTINCT a.[user], a.ID, a.Name, b.status
from master a
INNER JOIN scenario b ON a.ID = b.ID
WHERE
    b.scenarioID = (
           SELECT max(scenarioID) FROM scenario c2 WHERE c2.ID=c.ID)

主

ID    user    Name
425   John    Skyline
426   John    Violin
427   Joe     Pura

脚本

ID    ScenarioID    status
425   1             active
425   2             active
425   3             done
426   1             active
426   2             active
427   1             done

期望的输出

ID    user    Name    status
425   John    Skyline done
426   John    Violin  active
427   Joe     Pura    done

Answer 1

您可以通过CROSS APPLY查找每个值的最新值来执行此操作：

Select  M.ID, M.[User], M.Name, X.Status
From    [Master]    M
Cross Apply
(
    Select  Top 1 S.Status
    From    Scenario    S
    Where   S.ID = M.ID
    Order By S.ScenarioID Desc
) X

另一种方法是使用 a ROW_NUMBER() PARTITIONEDon theID和ORDEREDby ScenarioID DESC：

;With OrderedStatuses As
(
    Select  M.Id, M.[User], M.Name, S.Status,
            Row_Number() Over (Partition By S.Id Order By S.ScenarioID Desc) RN
    From    [Master]    M
    Join    Scenario    S   On  S.Id = M.Id
)
Select  Id, [User], Name, Status
From    OrderedStatuses
Where   RN = 1

Answer 2

这是使用 CTE 的稍微不同的公式，我通常发现它比子查询更容易阅读（当然，您的情况可能会有所不同）。

declare @Master table
(
    ID bigint,
    [user] varchar(16),
    Name varchar(16)
);

declare @Scenario table
(
    ID bigint,
    ScenarioID bigint,
    [status] varchar(16)
);

insert @Master values
    (425, 'John', 'Skyline'),
    (426, 'John', 'Violin'),
    (427, 'Joe', 'Pura');
insert @Scenario values
    (425, 1, 'active'),
    (425, 2, 'active'),
    (425, 3, 'done'),
    (426, 1, 'active'),
    (426, 2, 'active'),
    (427, 1, 'done');

with ReversedScenarioCTE as
(
    select
        ID,
        [status],
        rowNumber = row_number() over (partition by ID order by ScenarioID desc)
    from
        @Scenario
)
select
    M.ID,
    M.[user],
    M.Name,
    S.[status]
from
    @Master M
    inner join ReversedScenarioCTE S on
        M.ID = S.ID and
        S.rowNumber = 1;