Retrieving rows that have 2 columns matching and 1 different

<p>Below is my table called 'datapoints'. I am trying to retrieve instances where there are different instances of 'sensorValue' for the same 'timeOfReading' and 'sensorNumber'.</p><p>For example:</p><pre><br /><code> sensorNumber sensorValue timeOfReading<br /><br /> 5 5 6<br /> 5 5 6<br /> 5 6 10 <----same time/sensor diff value!<br /> 5 7 10 <----same time/sensor diff value!<br /></code><br /></pre><p>Should output: sensorNumber:5, timeOfReading: 10 as a result.</p><p><a href="http://ift.tt/1JfjfiI" rel="nofollow"><img src="http://ift.tt/1JfjfiI" alt="datapoints table" /></a></p><p>I understand this is a duplicate question, in fact I have one of the links provided below for references - however none of the solutions are working as my query simply never ends.</p><p>Below is my SQL code:</p><pre><br /><code>SELECT table1.sensorNumber, table1.timeOfReading<br />FROM datapoints table1<br />WHERE (SELECT COUNT(*)<br /> FROM datapoints table2<br /> WHERE table1.sensorNumber = table2.sensorNumber<br /> AND table1.timeOfReading = table1.timeOfReading <br /> AND table1.sensorValue != table2.sensorValue) > 1<br /> AND table1.timeOfReading < 20;<br /></code><br /></pre><p>Notice I have placed a bound for timeOfReading as low as 20. I also tried setting a bound for both table1 and table 2 as well but the query just runs until timeout without displaying results no matter what I put...</p><p>The database contains about 700mb of data, so I do not think I can just run this on the entire DB in a reasonable amount of time, I am wondering if this is the culprit?</p><p>If so how could I properly limit my query to run a search efficiently? If not what am doing wrong that this is not working?</p><p><a href="http://ift.tt/1Vpgqxp">Select rows having 2 columns equal value</a></p><p>EDIT: Error Code: 2013. Lost connection to MySQL server during query 600.000 sec</p><p>When I try to run the query again I get this error unless I restart Error Code: 2006. MySQL server has gone away 0.000 sec</p><br /><h2>Click here view more answers <a href="%20http://stackoverflow.com/questions/34525665/retrieving-rows-that-have-2-columns-matching-and-1-different">http://ift.tt/1JfjeeR</a></h2>