Question

我脑海中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：

位置
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（定义速度障碍）？我的第一个想法是将表加载到一个数组中，然后迭代数组以找到这些句点：

（伪C＃代码）

bool isOverSpeed = false;

for (int i =0;i<arr.Length;i++)
{
if (!isOverSpeed)
    if (arr[i].Velocity > 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，但有些“不是非常有效”。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？

Answer 1

您可以使用CTE（Common Table Expressions）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）。

受到关于SO的另一个问题的强烈启发：GROUP BY for continuous rows in SQL。

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

这些方面的东西应该适合你：

with CTE as (
    select
        ROW_NUMBER() over(order by [Time]) as RowNo
        , *
    from
        <table_name>
)
, MySpeedGroup as (
    select
        s.*
        ,(select
              max([Time])
          from
              CTE c
          where
              not exists (select * from CTE
                              where RowNo = c.RowNo-1
                              and Velocity > <speed_limit>
                              and c.Velocity > <speed_limit>)
              and c.[Time] <= s.[Time]) as GroupID
    from
        <table_name> 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) > <speed_limit>
order by
    minimum

Answer 2

简单，或者可以吗？

SELECT
  Location,
  Velocity,
  Time,
  CASE WHEN Velocity > @SpeedBarrier THEN 1 ELSE 0 END AS IsOverSpeed
FROM
  SpeedTable

Answer 3

我使用以下部分来获取一些数据（我在兼容模式80 atm上，因此我没有时间字段，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

Answer 4

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＆gt; speedLimit =真或速度＆lt; = speedLimit =假）超速从表哪里 speedLimit = yourGivenLimit

我没有对此进行测试，但我确信会有类似的事情。

4 个答案: