那些遇到过的问题

SQL 挑战 - 传感器阈值异常报告

SQL*_*tor 5 t-sql window-functions group-by

我添加了一个不使用窗口函数的解决方案和一个基准测试，其中包含一个低于 Martin's Answer 的大数据集

这是GROUP BY 使用不在 SELECT 列表中的列的后续线程- 这什么时候实用、优雅或强大？

在我对这一挑战的解决方案中，我使用了一个查询，该查询按不属于选择列表的表达式进行分组。当逻辑分组元素涉及来自其他行的数据时，这经常与窗口函数一起使用。

也许这是一个矫枉过正的例子，但我认为你可能会发现挑战本身很有趣。我会等待发布我的解决方案，也许你们中的一些人可以提出更好的解决方案。

挑战

我们有一个定期记录读数值的传感器表。无法保证采样时间处于单调间隔。

您需要编写一个查询来报告“异常”，这意味着传感器报告的读数超出阈值的次数，无论是低还是高。传感器报告超过或低于阈值的每个时间段都被视为“例外”。一旦读数恢复正常，异常结束。

示例表和数据

该脚本采用 T-SQL 格式，是我的培训材料的一部分。

这是 SQLFiddle 的链接。

------------------------------------------
-- Sensor Thresholds - 1 - Setup Example --
------------------------------------------

CREATE TABLE [Sensors]
(
    [Sensor] NVARCHAR(10) NOT NULL,
    [Lower Threshold] DECIMAL(7,2) NOT NULL,
    [Upper Threshold] DECIMAL(7,2) NOT NULL,
    CONSTRAINT [PK Sensors] 
        PRIMARY KEY CLUSTERED ([Sensor]),
    CONSTRAINT [CK Value Range]
        CHECK ([Upper Threshold] > [Lower Threshold])
);
GO

INSERT INTO [Sensors]
( 
    [Sensor] ,
    [Lower Threshold] ,
    [Upper Threshold]
)
VALUES  (N'Sensor A', -50, 50 ),
        (N'Sensor B', 40, 80),
        (N'Sensor C', 0, 100);
GO

CREATE TABLE [Measurements]
(
    [Sensor] NVARCHAR(10) NOT NULL,
    [Measure Time] DATETIME2(0) NOT NULL,
    [Measurement] DECIMAL(7,2) NOT NULL,
    CONSTRAINT [PK Measurements] 
        PRIMARY KEY CLUSTERED ([Sensor], [Measure Time]),
    CONSTRAINT [FK Measurements Sensors] 
        FOREIGN KEY ([Sensor]) 
        REFERENCES [Sensors]([Sensor])
);
GO

INSERT INTO [Measurements]
( 
    [Sensor] ,
    [Measure Time] ,
    [Measurement]
)
VALUES  ( N'Sensor A', N'20160101 08:00', -9), 
        ( N'Sensor A', N'20160101 09:00', 30), 
        ( N'Sensor A', N'20160101 10:30', 59), 
        ( N'Sensor A', N'20160101 23:00', 66),  
        ( N'Sensor A', N'20160102 08:00', 48), 
        ( N'Sensor A', N'20160102 11:30', 08), 
        ( N'Sensor B', N'20160101 08:00', 39), -- Note that this exception range has both over and under....
        ( N'Sensor B', N'20160101 10:30', 88), 
        ( N'Sensor B', N'20160101 13:00', 75), 
        ( N'Sensor B', N'20160102 08:00', 95),  
        ( N'Sensor B', N'20160102 17:00', 75), 
        ( N'Sensor C', N'20160101 09:00', 01), 
        ( N'Sensor C', N'20160101 10:00', -1),  
        ( N'Sensor C', N'20160101 18:00', -2), 
        ( N'Sensor C', N'20160101 22:00', -2), 
        ( N'Sensor C', N'20160101 23:30', -1);
GO
Run Code Online (Sandbox Code Playgroud)

预期结果

Sensor      Exception Start Time    Exception End Time  Exception Duration (minutes)    Min Measurement Max Measurement Lower Threshold Upper Threshold Maximal Delta From Thresholds
------      --------------------    ------------------  ----------------------------    --------------- --------------- --------------- --------------- -----------------------------
Sensor A    2016-01-01 10:30:00     2016-01-02 08:00:00 1290                            59.00           66.00           -50.00          50.00           16.00
Sensor B    2016-01-01 08:00:00     2016-01-01 13:00:00 300                             39.00           88.00           40.00           80.00           8.00
Sensor B    2016-01-02 08:00:00     2016-01-02 17:00:00 540                             95.00           95.00           40.00           80.00           15.00
Sensor C    2016-01-01 10:00:00     2016-01-01 23:30:00 810                             -2.00           -1.00           0.00            100.00          -2.00
*/
Run Code Online (Sandbox Code Playgroud)

Mar*_*ith 7

我可能会使用类似下面的东西。

它能够使用索引顺序并避免排序，直到它到达最终结果GROUP BY（对我来说，它使用流聚合）

原则上，实际上并不需要这个最后的分组操作。应该可以读取按流排序的输入流Sensor, MeasureTime并以流方式输出所需的结果，但我认为您需要为此编写 SQLCLR 过程。

WITH T1
     AS (SELECT m.*,
                s.[Lower Threshold],
                s.[Upper Threshold],
                within_threshold,
                start_group_flag = IIF(within_threshold = 0 AND LAG(within_threshold, 1, 1) OVER (PARTITION BY m.[Sensor] ORDER BY [Measure Time]) = 1, 1, 0),
                next_measure_time = LEAD([Measure Time]) OVER (PARTITION BY m.[Sensor] ORDER BY [Measure Time]),
                overage = IIF(Measurement > [Upper Threshold], Measurement - [Upper Threshold], 0),
                underage =IIF(Measurement < [Lower Threshold], Measurement - [Lower Threshold], 0)
         FROM   [Measurements] m
                JOIN [Sensors] s
                  ON m.Sensor = s.Sensor
                CROSS APPLY (SELECT IIF(m.[Measurement] BETWEEN s.[Lower Threshold] AND s.[Upper Threshold],1,0)) ca(within_threshold)),
     T2
     AS (SELECT *,
                group_number = SUM(start_group_flag) OVER (PARTITION BY [Sensor] ORDER BY [Measure Time] ROWS UNBOUNDED PRECEDING)
         FROM   T1
         WHERE  within_threshold = 0)
SELECT Sensor,
       [Exception Start Time] = MIN([Measure Time]),
       [Exception End Time] = MAX(ISNULL(next_measure_time, [Measure Time])),
       [Exception Duration (minutes)] = DATEDIFF(MINUTE, MIN([Measure Time]), MAX(ISNULL(next_measure_time, [Measure Time]))),
       [Min Measurement] = MIN(Measurement),
       [Max Measurement] = MAX(Measurement),
       [Lower Threshold],
       [Upper Threshold],
       [Maximal Delta From Thresholds] = IIF(MAX(overage) > -MIN(underage), MAX(overage), MIN(underage))
FROM   T2
GROUP  BY group_number,
          Sensor,
          [Lower Threshold],
          [Upper Threshold]
Run Code Online (Sandbox Code Playgroud)

在此处输入图片说明

Pau*_*ite 6

按Sensor, [Measure Time]顺序读取行的流式 SQL CLR 函数实现：

来源

using Microsoft.SqlServer.Server;
using System;
using System.Collections;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;

public partial class UserDefinedFunctions
{
    [SqlFunction(
        DataAccess = DataAccessKind.Read,
        FillRowMethodName = "GetExceptions_FillRow",
        IsDeterministic = true,
        IsPrecise = true,
        Name = "GetExceptions",
        SystemDataAccess = SystemDataAccessKind.None,
        TableDefinition =
            @"
            Sensor nvarchar(10) NULL,
            Exception_Start_Time datetime2(0) NULL,
            Exception_End_Time datetime2(0) NULL,
            Exception_Duration_Minutes integer NULL,
            Min_Measurement decimal (7,2) NULL,
            Max_Measurement decimal (7,2) NULL,
            Lower_Threshold decimal (7,2) NULL,
            Upper_Threshold decimal (7,2) NULL,
            Maximal_Delta_From_Thresholds decimal (7,2) NULL
            ")]
    public static IEnumerator GetExceptions
    (
        [SqlFacet(MaxSize = 256)] SqlString Instance,
        [SqlFacet(MaxSize = 128)] SqlString Database
    )
    {
        const string query =
            @"
            SELECT
                S.Sensor,
                S.[Lower Threshold],
                S.[Upper Threshold],
                M.[Measure Time],
                M.Measurement
            FROM dbo.Sensors AS S
            JOIN dbo.Measurements AS M
                ON M.Sensor = S.Sensor
            ORDER BY
                S.Sensor ASC,
                M.[Measure Time] ASC;
            ";

        var csb = new SqlConnectionStringBuilder
        {
            ApplicationName = "Thresholds.GetExceptions",
            ContextConnection = false,
            DataSource = Instance.Value,
            Enlist = false,
            InitialCatalog = Database.Value,
            IntegratedSecurity = true
        };

        using (var con = new SqlConnection(csb.ConnectionString))
        {
            con.Open();
            using (var cmd = new SqlCommand(query, con))
            {
                var reader = cmd.ExecuteReader(CommandBehavior.SingleResult | CommandBehavior.SequentialAccess);

                Record record = null;
                SensorException sensorException = null;

                while (reader.Read())
                {
                    record = new Record
                    {
                        Sensor = reader.GetSqlString(0),
                        LowerThreshold = reader.GetSqlDecimal(1),
                        UpperThreshold = reader.GetSqlDecimal(2),
                        MeasureTime = reader.GetDateTime(3),
                        Measurement = reader.GetSqlDecimal(4)
                    };

                    if (record.Measurement < record.LowerThreshold || record.Measurement > record.UpperThreshold)
                    {
                        if (sensorException == null)
                        {
                            sensorException = new SensorException
                            {
                                Sensor = record.Sensor,
                                Exception_Start_Time = record.MeasureTime,
                                Min_Measurement = record.Measurement,
                                Max_Measurement = record.Measurement,
                                Lower_Threshold = record.LowerThreshold,
                                Upper_Threshold = record.UpperThreshold
                            };
                        }
                        else
                        {
                            if (record.Measurement < sensorException.Min_Measurement)
                            {
                                sensorException.Min_Measurement = record.Measurement;
                            }

                            if (record.Measurement > sensorException.Max_Measurement)
                            {
                                sensorException.Max_Measurement = record.Measurement;
                            }
                        }
                    }
                    else
                    {
                        if (sensorException != null)
                        {
                            sensorException.Exception_End_Time = record.MeasureTime;
                            yield return sensorException;
                            sensorException = null;
                        }
                    }
                }

                // Final row
                if (sensorException != null)
                {
                    sensorException.Exception_End_Time = record.MeasureTime;
                    yield return sensorException;
                    sensorException = null;
                }
            }
        }
    }

    public static void GetExceptions_FillRow
    (
        Object obj,
        out SqlString Sensor,
        out DateTime Exception_Start_Time,
        out DateTime Exception_End_Time,
        out SqlInt32 Exception_Duration_Minutes,
        out SqlDecimal Min_Measurement,
        out SqlDecimal Max_Measurement,
        out SqlDecimal Lower_Threshold,
        out SqlDecimal Upper_Threshold,
        out SqlDecimal Maximal_Delta_From_Thresholds
    )
    {
        var sensorException = (SensorException)obj;
        Sensor = sensorException.Sensor;
        Exception_Start_Time = sensorException.Exception_Start_Time;
        Exception_End_Time = sensorException.Exception_End_Time;
        Exception_Duration_Minutes = Convert.ToInt32(Exception_End_Time.Subtract(Exception_Start_Time).TotalMinutes);
        Min_Measurement = sensorException.Min_Measurement;
        Max_Measurement = sensorException.Max_Measurement;
        Lower_Threshold = sensorException.Lower_Threshold;
        Upper_Threshold = sensorException.Upper_Threshold;

        var upperDiff = Max_Measurement > Upper_Threshold ? Max_Measurement - Upper_Threshold : 0;
        var lowerDiff = Min_Measurement < Lower_Threshold ? Lower_Threshold - Min_Measurement : 0;

        Maximal_Delta_From_Thresholds = upperDiff > lowerDiff ? upperDiff : lowerDiff;
    }

    internal class Record
    {
        internal SqlString Sensor { get; set; }
        internal SqlDecimal LowerThreshold { get; set; }
        internal SqlDecimal UpperThreshold { get; set; }
        internal DateTime MeasureTime { get; set; }
        internal SqlDecimal Measurement { get; set; }
    }

    internal class SensorException
    {
        internal SqlString Sensor { get; set; }
        internal DateTime Exception_Start_Time { get; set; }
        internal DateTime Exception_End_Time { get; set; }
        internal SqlDecimal Min_Measurement { get; set; }
        internal SqlDecimal Max_Measurement { get; set; }
        internal SqlDecimal Lower_Threshold { get; set; }
        internal SqlDecimal Upper_Threshold { get; set; }
    }
}
Run Code Online (Sandbox Code Playgroud)

部署脚本

创建汇编位（有点太长，无法发布内联）

注意：由于限制，这个程序集需要EXTERNAL_ACCESS权限，尽管它只从同一个数据库中读取。出于测试目的，创建 database 就足够了TRUSTWORTHY，尽管有充分的理由不在生产中这样做 - 而是对程序集进行签名。

CREATE OR ALTER FUNCTION dbo.GetExceptions 
(
    @Instance nvarchar(256), 
    @Database nvarchar(128)
)
RETURNS TABLE 
(
    Sensor nvarchar(10) NULL,
    [Exception Start Time] datetime2(0) NULL,
    [Exception End Time] datetime2(0) NULL,
    [Exception Duration (minutes)] integer NULL,
    [Min Measurement] decimal (7,2) NULL,
    [Max Measurement] decimal (7,2) NULL,
    [Lower Threshold] decimal (7,2) NULL,
    [Upper_Threshold] decimal (7,2) NULL,
    [Maximal Delta From Thresholds] decimal (7,2) NULL
)
ORDER (Sensor, [Exception Start Time])
AS EXTERNAL NAME Thresholds.UserDefinedFunctions.GetExceptions;
Run Code Online (Sandbox Code Playgroud)

询问

SELECT
    GE.Sensor,
    GE.[Exception Start Time],
    GE.[Exception End Time],
    GE.[Exception Duration (minutes)],
    GE.[Min Measurement],
    GE.[Max Measurement],
    GE.[Lower Threshold],
    GE.Upper_Threshold,
    GE.[Maximal Delta From Thresholds]
FROM dbo.GetExceptions(@@SERVERNAME, DB_NAME()) AS GE
ORDER BY
    GE.Sensor,
    GE.[Exception Start Time];
Run Code Online (Sandbox Code Playgroud)

需要参数以便函数知道如何连接到源数据。

执行计划

CLR 功能计划

结果

?????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? ?????????????????????????????????????????????
? 传感器 ？异常开始时间？异常结束时间？异常持续时间（分钟） ? 最小测量 ? 最大测量 ? 下限 ? 上限_阈值？来自阈值的最大增量 ?
?????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? ?????????????????????????????????????????????
? 传感器 A ? 2016-01-01 10:30:00 ？2016-01-02 08:00:00 ？1290？59.00？66.00？-50.00 ? 50.00 ? 16 点？
? 传感器 B ? 2016-01-01 08:00:00 ？2016-01-01 13:00:00 ？300 ? 39.00？88.00？40.00 ? 80.00 ? 8.00 ?
? 传感器 B ? 2016-01-02 08:00:00 ？2016-01-02 17:00:00 ？540？95.00？95.00？40.00 ? 80.00 ? 15.00 ?
? 传感器 C ? 2016-01-01 10:00:00 ？2016-01-01 23:30:00 ？810？-2.00 ? -1.00 ? 0.00 ? 100.00 ? 2.00 ?
?????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? ?????????????????????????????????????????????????????? ?????????????????????????????????????????????

归档时间：

查看次数：

280 次

最近记录：

6 年，9 月 前
相关归档
将 Where 子句与 Merge 一起使用 14
SQL Server：用通配符替换？ 10
添加一个新列并定义其在表格中的位置 7
左连接和左外连接的区别 5
加入时包含 NULL 行 4
SQL Server 2016 - 对性能不佳的查询发出过多的内存授予警告 4
我可以使用 Try_Cast 为我提供具有不同数据类型的查询结果列吗？ 2
我们可以用 UNION ALL 来交换逻辑或吗？ 2
复杂查询中的执行顺序 1
修改T-SQL获取结果 0
难疑归档
SQL Server 中的临时表和表变量有什么区别？ 465
MySQL 能否合理地对数十亿行进行查询？ 289
为读取性能配置 PostgreSQL 47
将选择结果写入 csv 文件 44
多列索引和性能 37
在哪里可以找到用于学习的数据库调优练习？ 32
复合主键是不好的做法吗？ 29
pg_stat_user_tables中n_live_tup和n_dead_tup是什么意思 26
备份 MySQL 数据库的最佳实践 26
如何在大表上使用 LEFT JOIN 优化非常慢的 SELECT 25