如果间隔小于 5 秒，则将几行合并为一行

Question

我正在尝试找到一个 SQL 查询，它可以让我将间隔小于 5 秒的 table 中的一些行合并为一行。例如，我有一个 table 如下所示：

Name    |    Time
==============================
John       2021-02-01 13:08:10
John       2021-02-01 13:08:12
John       2021-02-01 17:35:23
John       2021-02-07 11:16:31
Walt       2021-01-14 10:23:48
Joseph     2021-01-23 07:04:33
Walt       2021-01-14 10:23:51
Walt       2021-01-04 09:22:45

所以，我想要这样的结果：

Name    |    Time
==============================
John       2021-02-01
John       2021-02-01
John       2021-02-07
Walt       2021-01-14
Walt       2021-01-04
Joseph     2021-01-23

对于 John，有两行的间隔小于 5 秒，因此它们将在同一天合并为一行。沃尔特也是如此。

我可以使用 SQL 查询来做到这一点吗？

提前致谢。

Answer 1

您只需要检查下一个日期是否在当前行之后的 5 秒内，如果是，则删除该行。这可以通过 LEAD 分析函数来实现。

with a as (
  select 'John'   as name, convert(datetime, '2021-02-01 13:08:10', 120) as dt union all
  select 'John'   as name, convert(datetime, '2021-02-01 13:08:12', 120) as dt union all
  select 'John'   as name, convert(datetime, '2021-02-01 13:08:15', 120) as dt union all
  select 'John'   as name, convert(datetime, '2021-02-01 17:35:23', 120) as dt union all
  select 'John'   as name, convert(datetime, '2021-02-07 11:16:31', 120) as dt union all
  select 'Walt'   as name, convert(datetime, '2021-01-14 10:23:48', 120) as dt union all
  select 'Joseph' as name, convert(datetime, '2021-01-23 07:04:33', 120) as dt union all
  select 'Walt'   as name, convert(datetime, '2021-01-14 10:23:51', 120) as dt union all
  select 'Walt'   as name, convert(datetime, '2021-01-04 09:22:45', 120) as dt
)
, gap_size as (
  select
    name,
    dt,
    /*Check the difference between current row and the next row per name*/
    datediff(s,
      dt,
      lead(dt) over(partition by name order by dt asc)
    ) as within_5_secs_with_next
  from a
)
select
  name,
  cast(dt as date) as dt_date
from gap_size
where coalesce(within_5_secs_with_next, 10) >= 5
order by name, dt asc
GO

name   | dt_date   
:----- | :---------
John   | 2021-02-01
John   | 2021-02-01
John   | 2021-02-07
Joseph | 2021-01-23
Walt   | 2021-01-04
Walt   | 2021-01-14

db<>fiddle here

如果间隔小于 5 秒，则将几行合并为一行

Merge several rows into one if they have a gap less than a 5 seconds

sql

tsql

sql-server

gaps-and-islands