找到超速的时期？
我脑海里浮现出一些有趣的东西。 假设我们有一个表（在SQL Server中），如下所示：
- 地点
- 速度
- 时间
例如：
Location Velocity Time 1 40 1:20 2 35 2:00 3 45 2:05 4 50 2:30 5 60 2:45 6 48 2:55 7 40 3:00 8 35 3:15 9 50 3:20 10 70 3:30 11 50 3:35 12 40 3:40 假设速度障碍是40kph，输出是这样的
Starttime Endtime 2:05 3:00 3:20 3:35
确定超速时间的最佳方法是什么（定义了速度障碍）？ 我的第一个想法是将表加载到数组中，然后迭代数组以查找这些句点：
（伪C＃代码）
bool isOverSpeed = false; for (int i =0;i speedBarrier) { #insert the first record into another array. isOverSpeed = true; } if(isOverSpeed) if (arr[i].Velocity < speedBarrier) { #insert the record into that array isOverSpeed = false; } }
它有效，但有点“不太有效”。 是否有“更智能”的方式，例如T-SQL查询或其他算法来执行此操作？
您可以使用CTE（ 公用表表达式 ）来实现此目的。
下面的查询适用于SQL Server的Adventure Works演示表（“速度限制”为7）。
这受到另一个关于SO的问题的强烈启发： 对于SQL中的连续行，GROUP BY 。
with CTE as ( select ROW_NUMBER() over(order by SalesTaxRateID) as RowNo , * from Sales.SalesTaxRate ) , MyLogGroup as ( select l.* ,(select max(SalesTaxRateID) from CTE c where not exists (select * from CTE where RowNo = c.RowNo-1 and TaxRate > 7 and c.TaxRate > 7) and c.SalesTaxRateID <= l.SalesTaxRateID) as GroupID from Sales.SalesTaxRate l) select min(SalesTaxRateID) as minimum , max(SalesTaxRateID) as maximum , avg(TaxRate) from MyLogGroup group by GroupID having min(TaxRate) > 7 order by minimum
沿着这些方向的东西应该适合你：
with CTE as ( select ROW_NUMBER() over(order by [Time]) as RowNo , * from ) , MySpeedGroup as ( select s.* ,(select max([Time]) from CTE c where not exists (select * from CTE where RowNo = c.RowNo-1 and Velocity > and c.Velocity > ) and c.[Time] <= s.[Time]) as GroupID from l) select min([Time]) as minimum , max([Time]) as maximum , avg([Velocity]) -- don't know if you want this from MySpeedGroup group by GroupID having min(Velocity) > order by minimum
它不能那么简单，还是可以呢？
SELECT Location, Velocity, Time, CASE WHEN Velocity > @SpeedBarrier THEN 1 ELSE 0 END AS IsOverSpeed FROM SpeedTable
我已经使用以下部分来获取一些数据（我在兼容模式80 atm所以我没有时间字段并且使用INT作为时间戳）
DECLARE @Info TABLE (Location INT IDENTITY, Velocity INT, [Time] INT); INSERT INTO @Info (Velocity, [Time]) VALUES (40, 80); INSERT INTO @Info (Velocity, [Time]) VALUES (35, 120); INSERT INTO @Info (Velocity, [Time]) VALUES (45, 125); INSERT INTO @Info (Velocity, [Time]) VALUES (50, 150); INSERT INTO @Info (Velocity, [Time]) VALUES (60, 165); INSERT INTO @Info (Velocity, [Time]) VALUES (48, 175); INSERT INTO @Info (Velocity, [Time]) VALUES (40, 180); INSERT INTO @Info (Velocity, [Time]) VALUES (35, 195); INSERT INTO @Info (Velocity, [Time]) VALUES (50, 200); INSERT INTO @Info (Velocity, [Time]) VALUES (70, 210); INSERT INTO @Info (Velocity, [Time]) VALUES (50, 215); INSERT INTO @Info (Velocity, [Time]) VALUES (40, 220); INSERT INTO @Info (Velocity, [Time]) VALUES (45, 225); INSERT INTO @Info (Velocity, [Time]) VALUES (45, 230);
假设您的位置是必须通过的固定点，以便完成以下操作将产生所需的输出。 我已将其分解为多个阶段，以便明确每个部分的作用。
DECLARE @Limit INT; SET @Limit = 40; WITH Stage1 ([Location], [Velocity], [Time]) AS ( SELECT * FROM @Info WHERE [Velocity] > @Limit ), Stage2 (Start) AS ( SELECT [Time] FROM [Stage1] WHERE ([Location] - 1) NOT IN (SELECT [Location] FROM [Stage1]) ), Stage3 ([Start], [Stop]) AS ( SELECT [Start] , (SELECT MIN([Time]) FROM [Stage1] WHERE ([Location] + 1) NOT IN (SELECT [Location] FROM [Stage1]) AND [Time] > [Stage2].[Start]) FROM Stage2 ) SELECT * FROM Stage3
假设如果它匹配，那么将遵循以下SQL查询
选择位置，速度，时间，（速度> speedLimit = true或者速度<= speedLimit = false）从表中超速，其中speedLimit = yourGivenLimit
我没有测试过这个，但我确信它会做的事情。