Siyual Siyual - 28 days ago 10
SQL Question

Calculating a rolling count over a specified window

The sample data may help explain what I'm trying to do more than explaining it, so I'll begin with that.

Here's the data I'm currently working with:

+-------------------------+--------------+
| CallStart | CallDuration |
+-------------------------+--------------+
| 2017-09-15 09:15:15.313 | 00:01:28 |
| 2017-09-15 09:15:15.317 | 00:01:45 |
| 2017-09-15 09:16:45.603 | 00:01:31 |
| 2017-09-15 09:17:00.637 | 00:01:24 |
| 2017-09-15 09:18:20.853 | 00:01:42 |
| 2017-09-15 09:18:25.870 | 00:01:24 |
| 2017-09-15 11:27:05.117 | 00:00:59 |
| 2017-09-15 11:31:16.053 | 00:01:18 |
| 2017-09-15 11:34:41.627 | 00:01:00 |
| 2017-09-15 12:16:45.413 | 00:01:01 |
| 2017-09-15 12:18:15.820 | 00:01:05 |
| 2017-09-15 12:30:43.607 | 00:01:04 |
| 2017-09-15 12:31:48.817 | 00:00:55 |
| 2017-09-15 12:35:14.563 | 00:00:59 |
| 2017-09-15 12:42:10.947 | 00:00:43 |
| 2017-09-15 12:56:28.807 | 00:01:14 |
| 2017-09-15 13:05:10.643 | 00:00:37 |
| 2017-09-15 13:20:08.400 | 00:00:37 |
| 2017-09-15 14:30:12.607 | 00:00:59 |
| 2017-09-15 14:31:22.807 | 00:00:49 |
| 2017-09-15 15:19:47.240 | 00:01:07 |
| 2017-09-15 16:04:47.753 | 00:00:55 |
| 2017-09-15 16:58:08.080 | 00:00:55 |
| 2017-09-15 17:05:04.557 | 00:00:50 |
| 2017-09-15 17:20:42.753 | 00:00:58 |
| 2017-09-15 17:28:09.140 | 00:01:05 |
| 2017-09-15 17:39:46.690 | 00:00:38 |
| 2017-09-15 17:40:21.957 | 00:01:05 |
| 2017-09-15 17:43:47.570 | 00:01:08 |
| 2017-09-15 17:47:23.390 | 00:01:05 |
| 2017-09-15 17:47:28.410 | 00:00:56 |
| 2017-09-15 17:51:59.380 | 00:01:04 |
+-------------------------+--------------+


I am trying to get a rolling
COUNT(*)
for the number of occurrences in this data over a 15-minute timeframe. The expected result for this data would be the following:

+-------------------------+--------------+------------------+
| CallStart | CallDuration | DropsIn15Minutes |
+-------------------------+--------------+------------------+
| 2017-09-15 09:15:15.313 | 00:01:28 | 1 |
| 2017-09-15 09:15:15.317 | 00:01:45 | 2 |
| 2017-09-15 09:16:45.603 | 00:01:31 | 3 |
| 2017-09-15 09:17:00.637 | 00:01:24 | 4 |
| 2017-09-15 09:18:20.853 | 00:01:42 | 5 |
| 2017-09-15 09:18:25.870 | 00:01:24 | 6 |
| 2017-09-15 11:27:05.117 | 00:00:59 | 1 |
| 2017-09-15 11:31:16.053 | 00:01:18 | 2 |
| 2017-09-15 11:34:41.627 | 00:01:00 | 3 |
| 2017-09-15 12:16:45.413 | 00:01:01 | 1 |
| 2017-09-15 12:18:15.820 | 00:01:05 | 2 |
| 2017-09-15 12:30:43.607 | 00:01:04 | 3 |
| 2017-09-15 12:31:48.817 | 00:00:55 | 3 |
| 2017-09-15 12:35:14.563 | 00:00:59 | 3 |
| 2017-09-15 12:42:10.947 | 00:00:43 | 4 |
| 2017-09-15 12:56:28.807 | 00:01:14 | 2 |
| 2017-09-15 13:05:10.643 | 00:00:37 | 2 |
| 2017-09-15 13:20:08.400 | 00:00:37 | 2 |
| 2017-09-15 14:30:12.607 | 00:00:59 | 1 |
| 2017-09-15 14:31:22.807 | 00:00:49 | 2 |
| 2017-09-15 15:19:47.240 | 00:01:07 | 1 |
| 2017-09-15 16:04:47.753 | 00:00:55 | 1 |
| 2017-09-15 16:58:08.080 | 00:00:55 | 1 |
| 2017-09-15 17:05:04.557 | 00:00:50 | 2 |
| 2017-09-15 17:20:42.753 | 00:00:58 | 1 |
| 2017-09-15 17:28:09.140 | 00:01:05 | 2 |
| 2017-09-15 17:39:46.690 | 00:00:38 | 2 |
| 2017-09-15 17:40:21.957 | 00:01:05 | 3 |
| 2017-09-15 17:43:47.570 | 00:01:08 | 3 |
| 2017-09-15 17:47:23.390 | 00:01:05 | 4 |
| 2017-09-15 17:47:28.410 | 00:00:56 | 5 |
| 2017-09-15 17:51:59.380 | 00:01:04 | 6 |
+-------------------------+--------------+------------------+


Sample data:

Create Table #Calls
(
CallStart DateTime,
CallDuration Time(0)
);
Insert Into #Calls
Values (N'2017-09-15T09:15:15.313', N'00:01:28'),
(N'2017-09-15T09:15:15.317', N'00:01:45'),
(N'2017-09-15T09:16:45.603', N'00:01:31'),
(N'2017-09-15T09:17:00.637', N'00:01:24'),
(N'2017-09-15T09:18:20.853', N'00:01:42'),
(N'2017-09-15T09:18:25.87', N'00:01:24'),
(N'2017-09-15T11:27:05.117', N'00:00:59'),
(N'2017-09-15T11:31:16.053', N'00:01:18'),
(N'2017-09-15T11:34:41.627', N'00:01:00'),
(N'2017-09-15T12:16:45.413', N'00:01:01'),
(N'2017-09-15T12:18:15.82', N'00:01:05'),
(N'2017-09-15T12:30:43.607', N'00:01:04'),
(N'2017-09-15T12:31:48.817', N'00:00:55'),
(N'2017-09-15T12:35:14.563', N'00:00:59'),
(N'2017-09-15T12:42:10.947', N'00:00:43'),
(N'2017-09-15T12:56:28.807', N'00:01:14'),
(N'2017-09-15T13:05:10.643', N'00:00:37'),
(N'2017-09-15T13:20:08.4', N'00:00:37'),
(N'2017-09-15T14:30:12.607', N'00:00:59'),
(N'2017-09-15T14:31:22.807', N'00:00:49'),
(N'2017-09-15T15:19:47.24', N'00:01:07'),
(N'2017-09-15T16:04:47.753', N'00:00:55'),
(N'2017-09-15T16:58:08.08', N'00:00:55'),
(N'2017-09-15T17:05:04.557', N'00:00:50'),
(N'2017-09-15T17:20:42.753', N'00:00:58'),
(N'2017-09-15T17:28:09.14', N'00:01:05'),
(N'2017-09-15T17:39:46.69', N'00:00:38'),
(N'2017-09-15T17:40:21.957', N'00:01:05'),
(N'2017-09-15T17:43:47.57', N'00:01:08'),
(N'2017-09-15T17:47:23.39', N'00:01:05'),
(N'2017-09-15T17:47:28.41', N'00:00:56'),
(N'2017-09-15T17:51:59.38', N'00:01:04');


I can somewhat get this to work via the following:

Select CallStart,
CallDuration,
DropsIn15Minutes =
(
Select Count(*)
From #Calls C2
Where C2.CallStart Between DateAdd(Minute, -15, C1.CallStart)
And C1.CallStart
)
From #Calls C1


But, I would like to avoid the sub-query, in favor of a
COUNT(*) OVER ()
(or any other solution if possible) solution.

Is this possible to do? Or is the sub-query the right solution for this?

Answer Source

One way - which may perform better than a nested loops join on a range if the table is big - would be to first create a numbers table...

CREATE TABLE dbo.Numbers
(
N INT PRIMARY KEY
);

    WITH E1(N) AS 
    (
        SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
        SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
        SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
    )                                       -- 1*10^1 or 10 rows
    , E2(N) AS (SELECT 1 FROM E1 a, E1 b)   -- 1*10^2 or 100 rows
    , E4(N) AS (SELECT 1 FROM E2 a, E2 b)   -- 1*10^4 or 10,000 rows
    , E8(N) AS (SELECT 1 FROM E4 a, E4 b)   -- 1*10^8 or 100,000,000 rows
INSERT INTO dbo.Numbers
    SELECT TOP (60*60*24) -1 + ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS N FROM E8;

And then use something along the following lines.

WITH Calls
     AS (SELECT *,
                --pre-truncate all call starts to second precision
                DATEADD(SECOND, DATEDIFF(SECOND, '20000101', CallStart), '20000101') AS CallStart_sec
         FROM   #Calls),
     PreAgg
     AS (SELECT CallStart_sec,
                COUNT(*) AS Cnt
         FROM   Calls
         GROUP  BY CallStart_sec),
     Dates(D)
     --Todo - something else other than hardcoding the dates
     AS (SELECT CAST('2017-09-15' AS DATETIME2)),
     RT
     AS (SELECT *,
                SUM(Cnt) OVER (ORDER BY DATEADD(SECOND, N.N, Dates.D)) ROWS BETWEEN 900 PRECEDING AND CURRENT ROW) AS Cume
         FROM   Dates
                CROSS JOIN dbo.Numbers N
                LEFT JOIN PreAgg P
                  ON P.CallStart_sec = DATEADD(SECOND, N.N, Dates.D))
SELECT C.CallStart_sec AS CallStart,
       CallDuration,
       Cume AS DropsIn15Minutes
FROM   Calls C
       JOIN RT
         ON RT.CallStart_sec = C.CallStart_sec