使用上一行進行比較？

Question

我試圖找出一種比較SQL Server 2008中兩行的有效方法。我需要編寫一個查詢，查找Movement表中連續N次有Speed < 10的所有行。

表的結構是：

EVENTTIME 速度

如果數據是：

2012-02-05 13:56:36.980, 2 
2012-02-05 13:57:36.980, 11 
2012-02-05 13:57:46.980, 2 
2012-02-05 13:59:36.980, 2 
2012-02-05 14:06:36.980, 22 
2012-02-05 15:56:36.980, 2 

然後，它會返回行3/4（13：57：46.980/13 ：59：36.980）如果我查找了2個連續的行，並且如果我查找了三個連續的行，它將不會返回任何內容。數據的順序僅爲EventTime/DateTime。

你可以給我的任何幫助將是偉大的。我正在考慮使用遊標，但它們通常效率很低。而且，這個表格大約有10m行，所以效率越高越好！ :)

謝謝！

Answer 1

DECLARE 
    @n    INT, 
    @speed_limit INT 
SELECT 
    @n    = 5, 
    @speed_limit = 10 

;WITH 
    partitioned AS 
(
    SELECT 
    *, 
    CASE WHEN speed < @speed_limit THEN 1 ELSE 0 END AS PartitionID 
    FROM 
    Movement 
) 
, 
    sequenced AS 
(
    SELECT 
    ROW_NUMBER() OVER (      ORDER BY EventTime) AS MasterSeqID, 
    ROW_NUMBER() OVER (PARTITION BY PartitionID ORDER BY EventTime) AS PartIDSeqID, 
    * 
    FROM 
    partitioned 
) 
, 
    filter AS 
(
    SELECT 
    MasterSeqID - PartIDSeqID AS GroupID, 
    MIN(MasterSeqID)    AS GroupFirstMastSeqID, 
    MAX(MasterSeqID)    AS GroupFinalMastSeqID 
    FROM 
    sequenced 
    WHERE 
    PartitionID = 1 
    GROUP BY 
    MasterSeqID - PartIDSeqID 
    HAVING 
    COUNT(*) >= @n 
) 
SELECT 
    sequenced.* 
FROM 
    filter 
INNER JOIN 
    sequenced 
    ON sequenced.MasterSeqID >= filter.GroupFirstMastSeqID 
    AND sequenced.MasterSeqID <= filter.GroupFinalMastSeqID 

替代最後步驟（由@叔克勞森-DK啓發），以避免額外的JOIN。我會測試兩個看看哪個更高性能。

, 
    filter AS 
(
    SELECT 
    MasterSeqID - PartIDSeqID        AS GroupID, 
    COUNT(*) OVER (PARTITION BY MasterSeqID - PartIDSeqID) AS GroupSize, 
    * 
    FROM 
    sequenced 
    WHERE 
    PartitionID = 1 
) 
SELECT 
    * 
FROM 
    filter 
WHERE 
    GroupSize >= @n 

Answer 2

declare @t table(EventTime datetime, Speed int) 
insert @t values('2012-02-05 13:56:36.980', 2) 
insert @t values('2012-02-05 13:57:36.980', 11) 
insert @t values('2012-02-05 13:57:46.980', 2) 
insert @t values('2012-02-05 13:59:36.980', 2) 
insert @t values('2012-02-05 14:06:36.980', 22) 
insert @t values('2012-02-05 15:56:36.980', 2) 

declare @N int = 1 

;with a as 
(
    select EventTime, Speed, row_number() over (order by EventTime) rn from @t 
), b as 
(
    select EventTime, Speed, 1 grp, rn from a where rn = 1 
    union all 
    select a.EventTime, a.Speed, case when a.speed < 10 and b.speed < 10 then grp else grp + 1 end, a.rn 
    from a join b on a.rn = b.rn+1 
), c as 
(
    select EventTime, Speed, count(*) over (partition by grp) cnt from b 
) 
select * from c 
where cnt > @N 
OPTION (MAXRECURSION 0) -- Thx Dems 

Answer 3

幾乎相同IDEEA作爲民主黨，有一點不同：

select * from (
select eventtime, speed, rnk, new_rnk, 
     rnk - new_rnk, 
     max(rnk) over (partition by speed, new_rnk-rnk) - 
     min(rnk) over (partition by speed, new_rnk-rnk) + 1 as no_consec 
    from (
    select eventtime, rnk, speed, 
      row_number() over (partition by speed order by eventtime) as new_rnk 
    from (
      select eventtime, speed, 
      row_number() over (order by eventtime) as rnk 
      from a 
     ) a 
    where a.speed < 5 
) 
order by eventtime 
) 
where no_consec >= 2; 

5是限速和2是分鐘數目的連續事件。 爲了簡化寫入創建數據庫，我將日期設置爲數字。

SQLFIDDLE

編輯：

要回答的意見，我在第一個內部查詢添加三列。要獲得第一行，您需要將WHERE子句添加一個pos_in_group = 1，距離在您的手指上。

SQLFIDDLE

select eventtime, speed, min_date, max_date, pos_in_group 

from (
    select eventtime, speed, rnk, new_rnk, 
     rnk - new_rnk, 
     row_number() over (partition by speed, new_rnk-rnk order by eventtime) pos_in_group, 
     min(eventtime) over (partition by speed, new_rnk-rnk) min_date, 
     max(eventtime) over (partition by speed, new_rnk-rnk) max_date, 
     max(rnk) over (partition by speed, new_rnk-rnk) - 
     min(rnk) over (partition by speed, new_rnk-rnk) + 1 as no_consec 
    from (
    select eventtime, rnk, speed, 
      row_number() over (partition by speed order by eventtime) as new_rnk 
    from (
      select eventtime, speed, 
      row_number() over (order by eventtime) as rnk 
      from a 
     ) a 
    where a.speed < 5 
    ) 
    order by eventtime 
) 
where no_consec > 1;