SQL how to group in time periods

问题

I'm trying to group data in time periods. Each period is 5 minutes and I'd like to see what was happening every 5 minutes from 08:00 to 18:00.

I have created a table that has all the time periods in that time range. E.g.:

StartTime           EndTime             IsBusinessHours
08:40:00.0000000    08:45:00.0000000    1
08:45:00.0000000    08:50:00.0000000    1
08:50:00.0000000    08:55:00.0000000    1
08:55:00.0000000    09:00:00.0000000    1

etc.

Select 
    TimeDimension.[StartTime],
    TimeDimension.[EndTime],
    activity.[Description],
    activity.[StartTime]
From
    TimeDimension 
    Full Outer Join Activity 
       on (
              Convert(varchar,activity.StartTime,108) >= Convert(varchar,TimeDimension.starttime, 108) 
          And Convert(varchar,activity.StartTime,108) <= Convert(varchar,TimeDimension.endtime, 108)
       )
Where               
    activity.Date = @DateParam 
And TimeDimension.isbusinesshours = 1

I expect to have data grouped by 5 minute time periods, but what I get is:

08:20:00.0000000    08:25:00.0000000 Some activity
08:30:00.0000000    08:35:00.0000000 Some activity
08:45:00.0000000    08:50:00.0000000 Three activities in this time period. First
08:45:00.0000000    08:50:00.0000000 Three activities in this time period. Second 
08:45:00.0000000    08:50:00.0000000 Three activities in this time period. Third

When what I'd like to see is:

08:20:00.0000000    08:25:00.0000000 Some activity
08:25:00.0000000    08:30:00.0000000 NULL
08:30:00.0000000    08:35:00.0000000 Some activity
08:35:00.0000000    08:40:00.0000000 NULL
08:45:00.0000000    08:50:00.0000000 Three activities in this time period. First
08:45:00.0000000    08:50:00.0000000 Three activities in this time period. Second 
08:45:00.0000000    08:50:00.0000000 Three activities in this time period. Third

This means that I'm displaying time periods when some activities took place, rather than all time periods in that range. I have called a table TimeDimension - but I'm not sure whether this is correct. Gut feeling tells me that this is something to do with analysis services.

Thank you

回答1:

Note 1: Doing DATETIME arithmetic using VARCHAR yields poor performance.

Note 2: You have an OUTER JOIN but then a WHERE clause that doesn't account for NULLs.

This is what I'd use...

WITH
  FilteredActivity AS
(
  SELECT
    Description,
    DATEADD(DAY, -DATEDIFF(DAY, 0, StartTime), StartTime) AS StartTime
  FROM
    Activity
  WHERE
    Date = @DateParam
)

SELECT
  TimeDimension.[StartTime],
  TimeDimension.[EndTime],
  activity.[Description],
  activity.[StartTime]
FROM
  TimeDimension
LEFT JOIN
  FilteredActivity AS [Activity]
    ON  Activity.StartTime >= TimeDimension.StartTime
    AND Activity.StartTime <  TimeDimension.EndTime
WHERE
  TimeDimension.isbusinesshours = 1

CTE Filtering

The CTE at the start filters Activity to just one date
This avoids the condition in your WHERE clause that plays poorly with OUTER JOINs

CTE Formatting

The CTE also strips the StartTime down to just a TimePart
The DATEADD/DATEDIFF business is only need if StartTime includes the DATE as well
If it is already just the time, just use StartTime

Exclusive vs Inclusive EndTime

I have < EndTime rather than <= EndTime
This assume intervals in the form of 08:00 to 08:05 and 08:05 to 08:10, etc
Having the EndTime as "the first time you don't want to include" can make things easier
No more rounding Activity.StartTime down to the nearest minute, for example
And no strange intervals of 08:00 to 08:04, etc

An alternative to using Exclusive EndTime values is to round your Activity.StartTime values to the nearest minute. Rather than using strings, the folowing does it using DateTime functions...
- DATEADD(minute, DATEDIFF(minute, 0, Activity.StartTime), 0)

回答2:

You say you want to group the results but you are not applying a GROUP to the query.

However, if you aggregate the results you will lose the distinct information you are also wanting (Description, StartDate) unless they match the other records in the group.

As Scorpi0 commented, a sample of the output you want would be useful.

回答3:

You have a filter on the activity table: activity.Date = @DateParam.

It prevents from getting every row of the TimeDimension table. Put the filter in the join clause and you will see all your datas.

Select 
    TimeDimension.[StartTime],
    TimeDimension.[EndTime],
    activity.[Description],
    activity.[StartTime]
From
    TimeDimension 
    Full Outer Join Activity 
       on (
              Convert(varchar,activity.StartTime,108) >= Convert(varchar,TimeDimension.starttime, 108) 
          And Convert(varchar,activity.StartTime,108) <= Convert(varchar,TimeDimension.endtime, 108)
          And activity.Date = @DateParam 
       )
Where TimeDimension.isbusinesshours = 1

Or you can do also:

Select 
    TimeDimension.[StartTime],
    TimeDimension.[EndTime],
    activity.[Description],
    activity.[StartTime]
From
    TimeDimension 
    Full Outer Join Activity 
       on (
              Convert(varchar,activity.StartTime,108) >= Convert(varchar,TimeDimension.starttime, 108) 
          And Convert(varchar,activity.StartTime,108) <= Convert(varchar,TimeDimension.endtime, 108)
       )
Where TimeDimension.isbusinesshours = 1
And (activity.Date Is Null Or activity.Date = @DateParam)

回答4:

You need to move activity time condition from common Where clause into Join condition, like so:

Select 
    TimeDimension.[StartTime],
    TimeDimension.[EndTime],
    activity.[Description],
    activity.[StartTime]
From
    TimeDimension 
    Full Outer Join Activity 
       on (
              Convert(varchar,activity.StartTime,108) >= Convert(varchar,TimeDimension.starttime, 108) 
          And Convert(varchar,activity.StartTime,108) <= Convert(varchar,TimeDimension.endtime, 108)
And activity.Date = @DateParam
       )
Where               
    TimeDimension.isbusinesshours = 1

来源：https://stackoverflow.com/questions/6909844/sql-how-to-group-in-time-periods

标签

sql

time

group-by

grouping