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Asked: 2026-05-13T05:36:39+00:00

Given a table that looks like this: sensor_id | time | voltage ———–+————————+———— 12292

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Given a table that looks like this:

 sensor_id |          time          |  voltage
-----------+------------------------+------------
     12292 | 2009-12-01 00:50:04-07 |       2270
     12282 | 2009-12-01 00:50:04-07 |      93774
     12192 | 2009-12-01 00:50:04-07 |       9386
     12609 | 2009-12-01 00:50:05-07 |          0
     12566 | 2009-12-01 00:50:08-07 |          0
     12659 | 2009-12-01 00:50:19-07 |        540
     12660 | 2009-12-01 00:50:19-07 |        550
     12661 | 2009-12-01 00:50:19-07 |        510
     12656 | 2009-12-01 00:50:19-07 |      30240
     12657 | 2009-12-01 00:50:19-07 |      14930
     12658 | 2009-12-01 00:50:19-07 |      17420
     11820 | 2009-12-01 00:50:26-07 |       1.38
     11832 | 2009-12-01 00:50:28-07 |      1.359
     12768 | 2009-12-01 00:50:33-07 |     636588
     13192 | 2009-12-01 00:50:34-07 |      1.401
         .                        .            .
         .                        .            .
         .                        .            .

There are times when you will get records looking like:

     12292 | 2009-12-01 00:50:04-07 |       2270
     12282 | 2009-12-01 00:50:04-07 |      93774
     12192 | 2009-12-01 00:50:04-07 |       9386
     12609 | 2009-12-01 00:50:05-07 |          0
     12566 | 2009-12-01 00:50:08-07 |          0
     12659 | 2009-12-01 00:50:19-07 |        540     *
     12659 | 2009-12-01 00:50:45-07 |        541     *
     12660 | 2009-12-01 00:50:19-07 |        550
     12661 | 2009-12-01 00:50:19-07 |        510
     12656 | 2009-12-01 00:50:19-07 |      30240
     12657 | 2009-12-01 00:50:19-07 |      14930
     12658 | 2009-12-01 00:50:19-07 |      17420
     11820 | 2009-12-01 00:50:26-07 |       1.38     #
     11832 | 2009-12-01 00:50:28-07 |      1.359
     11820 | 2009-12-01 00:50:28-07 |        1.3     #
     12768 | 2009-12-01 00:50:33-07 |     636588
     13192 | 2009-12-01 00:50:34-07 |      1.401
         .                        .            .
         .                        .            .
         .                        .            .

Notice the stared and hashed lines. Each are readings taken in the same minute, but i need only one value per minute, preferably the max value.
I tried:


select sensor_id, read_time, voltage 
from table 
where (sensor_id, read_time) 
in (select sensor_id, max(read_time) 
    from table 
    group by sensor_id);

This obviously doesn’t work, but I think I’m on the right track?

For those interested the final code looks like: 


select sensor_id, date_trunc('minute', read_time), max(voltage) 
from table 
group by sensor_id, date_trunc('minute', read_time) 
order by date_trunc('minute', read_time);
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1 Answer

  1. Editorial Team

    You have to group By an expression that “defines” the one minute buckets you want the maximum values in:

    select sensor_id, DateHourMinuteFunction(read_time), Max(voltage) 
from table 
Group By sensor_id, DateHourMinuteFunction(read_time)

    Where DateHourMinuteFunction(read_time) is some function or Sql Expression in your database that will return an expression that is the same for any read_time in the same minute(i.e., it needs to strip off the seconds values)

    Can your database convert a date time to a string? If so, then at a minimum write an expression that converts it to a string, formatted as Month day year, hour, minute, second, and then strip off the seconds part…

    Assuming what you already have in the datetime column was a string, then just use substring on it… 

    select sensor_id, SubString(Cast(read_time as varChar(22)), 0, 16), Max(voltage) 
from table 
Group By sensor_id, SubString(Cast(read_time as varChar(22)), 0, 16)
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