SQL查询按时间间隔

Question

So I have used this post as a reference, however I would like to count all the rows based on a 15 minute time period.

Here is what I have so far:

SELECT      DateAdd(minute, DateDiff(minute, 0, [datetime]), 0) as Timestamp, 
            Count(*) as Tasks
FROM        [table]
GROUP BY    DateAdd(minute, DateDiff(minute, 0, [datetime]), 0)
ORDER BY    Timestamp

This is great for getting rows per minute, however I need 15 minutes... So I change:

DateAdd(minute, DateDiff(minute, 0, [datetime]), 0)

to

DateAdd(minute, DateDiff(minute, 0, [datetime]), 15)

however that is just pushing the date 15 days ahead.

Any help is appreciated!

Answer 1

To get 15 minutes, divide by 15 (and then multiply again):

SELECT      DateAdd(minute, 15*(DateDiff(minute, 0, [datetime]) / 15), 0
                   ) as Timestamp, 
            Count(*) as Tasks
FROM        [table]
GROUP BY    (DateDiff(minute, 0, [datetime]) / 15)
ORDER BY    Timestamp;

SQL Server does integer division. If you want to be unambiguous about your intentions, use FLOOR() .

Answer 2

SELECT  ROUND(DATEDIFF(SECOND,{d '1970-01-01'},[datetime])/(15 * 60),0) as Timestamp, 
            Count(*) as Tasks
FROM   [table]
GROUP BY    ROUND(DATEDIFF(SECOND,{d '1970-01-01'},[datetime])/(15 * 60),0)
ORDER BY    Timestamp 

Answer 3

Here is an alternative in case integer division causes an issue for you. It casts the datetime as a float and then uses floor().

SELECT      convert(varchar,cast(round(floor(cast([datetime] as float(53))*24*4)/(24*4),5) as smalldatetime),108)  as Timestamp, 
            Count(*) as Tasks
FROM        [table]
GROUP BY    convert(varchar,cast(round(floor(cast([datetime] as float(53))*24*4)/(24*4),5) as smalldatetime),108)
ORDER BY    Timestamp

I normally change the (24*4) to 96 (the number of 15 minute intervals in a day), but thought I'd leave it so people can see how to adapt it for other time periods.