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POPSQL select max value per minute per id for multiple values a minute per id?
 

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    <p>Given a table that looks like this:</p> <pre> 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 . . . . . . . . . </pre> <p>There are times when you will get records looking like:</p> <pre> 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 . . . . . . . . . </pre> <p>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:</p> <pre><code> 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); </code></pre> <p>This obviously doesn't work, but I think I'm on the right track?</p> <p><hr> For those interested the final code looks like: </p> <pre> <code> 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); </code> </pre>
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