检索SQL中的最新活动

Question

美好的一天

我有一个在不同日期发生的活动表，可以使用查询（T-SQL）检索：

Select  Activities.activityid,
        Activities.ActivityTypeCode,
        Activities.ActivityDate,
        Activities.SequenceOrder,
        Activities.Place,
        Activities.TypeOfPlace
From Activities
Where Activities.ActivityTypeCode In ('LOST', 'FOUND', 'NOT SEEN')

问题：如何检索最新的？还是最近的第二次？

对于您的信息：有一个名为sequenceOrder的字段，用于跟踪输入活动时的顺序。

请帮忙。

Answer 1

将GROUP BY子句与子查询一起使用

SELECT * 
FROM Activities
WHERE sequenceOrder IN (
              SELECT MAX(SequenceOrder) 
              FROM Activities
              WHERE ActivityTypeCode In ('LOST', 'FOUND', 'NOT SEEN')
              GROUP BY ActivityTypeCode 
)

如果，您希望获得（LOST，FOUND，NOT SEEN）中唯一最活跃的活动，则从子查询中删除GROUP BY子句。

Answer 2

select * from (
Select  Activities.activityid,
    Activities.ActivityTypeCode,
    Activities.ActivityDate,
    Activities.SequenceOrder,
    Activities.Place,
    Activities.TypeOfPlace,
    row_number() over (partition by Activities.ActivityTypeCode order by Activities.SequenceOrder) [rn]
From Activities
Where Activities.ActivityTypeCode In ('LOST', 'FOUND', 'NOT SEEN')
) a where rn = 1 --2 if you want second most recent

Answer 3

使用ROW_NUMBER：

SELECT
    activityid,
    ActivityTypeCode,
    ActivityDate,
    SequenceOrder,
    Place,
    TypeOfPlace
FROM
(
    SELECT *,
        ROW_NUMBER() OVER (ORDER BY SequenceOrder DESC) rn
    FROM Activities
    WHERE ActivityTypeCode IN ('LOST', 'FOUND', 'NOT SEEN')
) t
WHERE rn = 1;

这种方法的优点是，如果你想要第二个最近的事件，我们可以使用WHERE rn = 2。

请注意，如果序列顺序中的值可能存在关联，那么我们可能希望使用秩函数而不是行号。

您可以将上述查询放入CTE（公用表表达式）：

WITH cte AS (
    SELECT
        activityid,
        ActivityTypeCode,
        ActivityDate,
        SequenceOrder,
        Place,
        TypeOfPlace
    FROM
    (
        SELECT *,
            ROW_NUMBER() OVER (ORDER BY SequenceOrder DESC) rn
        FROM Activities
        WHERE ActivityTypeCode IN ('LOST', 'FOUND', 'NOT SEEN')
    ) t
    WHERE rn = 1
)

SELECT * FROM cte;

但请注意，从性能的角度来看，在子查询中包装查询是不可取的。相反，只需定制我的原始查询以满足您的需求。