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POSorting data from tables according to time with a level of accuracy in datetime
 

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  1. POSorting data from tables according to time with a level of accuracy in datetime
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    <p>I have two tables containing datetime and double. </p> <p>Which looks like this:</p> <pre><code>mysql&gt; select * from ONE; | mysql&gt; select * from TWO; +---------------------+----------+ | +---------------------+----------+ | date | value | | | date | value | +---------------------+----------+ | +---------------------+----------+ | 2002-03-18 10:30:02 | -181.241 | | | 2002-03-18 10:30:00 | -188.192 | | 2002-03-18 10:30:06 | -180.673 | | | 2002-03-18 10:30:04 | -187.619 | | 2002-03-18 10:30:10 | -180.055 | | | 2002-03-18 10:30:08 | -187.032 | | 2002-03-18 10:30:14 | -179.459 | | | 2002-03-18 10:30:12 | -186.418 | | 2002-03-18 10:30:18 | -178.801 | | | 2002-03-18 10:30:16 | -185.807 | </code></pre> <p>I'm trying to perform a query on the values from each of the tables with a common date column (using ONE.date as reference). However, in some cases the measurements does not have symmetric date. Above is an example of such a period (this is worst case scenario), here the values from table TWO corresponds to the values in table ONE two seconds later. </p> <p>In order to sort the values of the two tables according to the time, I want to allow a "sorting accuracy", set to be a maximum time difference between the measurements of one "event". This accuracy is in this case 2 seconds. </p> <p>How I wan't it to look: If the time difference between ONE.data and TWO.date is less than +- 2 seconds; join the value from TWO in ONE: </p> <pre><code>mysql&gt; select * from ONE; +---------------------+----------+-----------+ | date | valueONE | valueTWO | +---------------------+----------+ ----------+ | 2002-03-18 10:30:02 | -181.241 | -188.192 | | 2002-03-18 10:30:06 | -180.673 | -187.619 | | 2002-03-18 10:30:10 | -180.055 | -187.032 | | 2002-03-18 10:30:14 | -179.459 | -186.418 | | 2002-03-18 10:30:18 | -178.801 | -185.807 | </code></pre> <p>If the difference is more than +- 2 seconds, discard the measurement. This is what I have tried, however the query below just times out.</p> <pre><code>SELECT ONE.date, ONE.value, TWO.date, TWO.value FROM ONE join TWO on ONE.date = TWO.date+INTERVAL 1 SECOND or ONE.date = TWO.date </code></pre> <p>Is it possible to have a IF sentence inside the join statement such that if </p> <pre><code> if SELECT TIMESTAMPDIFF(SECOND,'2002-03-18 10:30:02','2002-03-18 10:30:00') &lt;= 2, then join </code></pre>
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    1. USLightness Races in Orbit
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    1. COIn your example, the timestamps in TWO also correspond to timestamps in ONE, but two seconds later. It seems you want the time series in ONE to take the lead in assembling the result set. Is that correct? Should the JOIN look both into the future and the past when selecting rows from TWO to match rows from ONE? Also, what do you want to happen if there are several rows in TWO within match- range of a single row in ONE, or vice versa?
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    2. COThanks for showing interest. The answer by fthiella was what I needed. However you make excellent points. Yes I chose ONE to be the reference (taking the lead in assembling the result), and yes I tried to make the join statement look both forward and backward when selecting the rows.. Lastly, good point. This might be a problem in another situation, however, in my dataset there would never be values with timestamps closer than 3.95 seconds. Thanks
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