Question

I have something like this:

 SELECt *
   FROM (
        SELECT prodid, date, time, tmp, rowid
          FROM live_pilot_plant
         WHERE date BETWEEN CONVERT(DATETIME, '3/19/2012', 101)
           AND CONVERT(DATETIME, '3/31/2012', 101)
         ) b
  WHERE b.rowid % 400 = 0

FYI: The reason for the convert in the where clause, is because my date is stored as a varchar(10), I had to convert it to datetime in order to get the correct range of data. (I tried a bunch of different things and this worked)

I’m wondering how I can return the data I want every 4 hours during those selected dates. I have data collected approximately every 5 seconds (with some breaks in data) – ie data wasn’t collected during a 2 hour period, but then continues at 5 second increments.

In my example I just used a modulo with my rowid – and the syntax works, but as I mentioned above there are some periods where data isnt collected so using logic like: if you take data every 5 seconds and multiple that by 4 hours you can approximately say how many rows are in between wont work.

My time column is a varchar column and is in the form hh:mm:ss

My ideal output is:

  | prodid  | date       | time      |  tmp  |
  |    4    | 3/19/2012  | 10:00:00  |  2.3  |
  |    7    | 3/19/2012  | 14:00:24  |  3.2  |

As you can see I can be a bit off (in terms of seconds) – I more so need the approximate value in terms of time.

Thank you in advance.

Answer 1

This should work

select prodid, date, time, tmp, rowid
from live_pilot_plant as lpp
inner join (

select min(prodid) as prodid                     -- is prodid your PK?? if not change it to rowid or whatelse is your PK
    from live_pilot_plant
    WHERE date BETWEEN CONVERT(DATETIME, '3/19/2012', 101)  -- or whatever you want
                   AND CONVERT(DATETIME, '3/31/2012', 101)  -- for better performance it is on the inner select
    group by date, 
    floor(                                       -- floor makes the trick
    convert(float,convert(datetime, time))       -- assumes "time" column is a varchar containing data like '19:23:05'
    * 6                                          -- 6 comes form 24 hours / 4 hours
    )

) as filter on lpp.prodid = filter.prodid        -- if prodid is not the PK also correct here.

A side note for everyone else who have date + time data in only one datetime field, suppose named “when_it_was”, the group by can be as simple as:

group by floor(when_it_was * 6)                  -- again, 6 comes from 24/4