Question

我有三张桌子：

Measurements (MeasureID, Time, Distance, Value)
Events(EventID, Time Value)
EventValues (EventDataID, EventID, Type, Value)

我需要获得每个测量，最近的事件（过去）及其相关的事件值数据。

我当前的查询非常难看：

SELECT 
    M.*,
    (SELECT TOP 1 EV.value FROM [Event] E JOIN EventValues EV ON E.EventID = EV.EventID 
     WHERE M.Time >= E.Time ORDER BY M.Time-E.Time) AS Data,
FROM [Measure] M 
ORDER BY M.Distance

它只允许我从EventValues表中选择一列（我需要更多）

有没有办法可以使用连接来完成？

编辑：我还需要从测量表中选择所有条目，即使它们位于第一个事件之前（即只选择连接的空数据）

Answer 1

您可以使用CROSS APPLY。

SELECT  
    M.*, Data.* 
FROM [Measure] M 
CROSS APPLY
     (SELECT TOP 1 EV.* FROM [Event] E JOIN EventValues EV ON E.EventID = EV.EventID  
     WHERE M.Time >= E.Time ORDER BY E.Time DESC) AS Data
ORDER BY M.Distance

Answer 2

尝试这样的事情（未经测试）

SELECT * FROM
(
    SELECT M.*, E.*, EV.EventDataID, EV.Type, EV.Value,
        Rank() over (Partition BY M.MeasureID order by M.Time - E.Time) as Rank
    FROM [Measure] M 
    INNER JOIN [Event] E ON M.Time >= E.Time
    INNER JOIN EventValues EV ON E.EventID = EV.EventID
) T
WHERE Rank = 1

修改

SELECT * FROM ( SELECT M.*, E.*, EV.EventDataID, EV.Type, EV.Value, Rank() over (Partition BY M.MeasureID order by M.Time - E.Time) as Rank FROM [Measure] M LEFT JOIN [Event] E ON M.Time >= E.Time LEFT JOIN EventValues EV ON E.EventID = EV.EventID ) T WHERE Rank = 1

SQL加入以获取最新记录

2 个答案: