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POSeparating/Sorting single column values into several columns using case function
 

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  1. POSeparating/Sorting single column values into several columns using case function
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    <p>I have two tables that I want to join and split with a case function depending on the values in one of the columns. (I know, sounds weird so let me explain)</p> <p>It's a process where I run separate batches. Every batch has several samples that are measured in instances of voltage readings in several locations. My two tables looks like this:</p> <pre><code>Sample Readings id id BatchesID SampleID ... voltage ... location </code></pre> <p>When a batch is run, it takes one sample at a time and for every location (25 locations) it takes about 20 readings of the voltage before moving on to the next one.</p> <p>I want to look at one batch at a time, and for every Sample.id, I want to gather the AVG(voltage) for all the locations. My table for Readings turns out like:</p> <pre><code>SampleID location voltage 1 1 5.23 1 1 4.53 ... ... ... 1 25 7.89 2 1 4.96 2 1 5.04 ... ... ... 2 25 6.09 ... </code></pre> <p>But I want it to look like:</p> <pre><code>SampleID avg_v_for_1 avg_v_for_2 ... avg_v_for_25 1 4.73 5.24 ... 6.35 2 3.87 4.76 ... 9.32 ... ... ... ... ... 200 6.73 3.87 ... 8.23 </code></pre> <p>Basically, what I want to do is for every separate sample, I want to take the average voltage for all the measurements in every location and put in on a single row. What my current syntax looks like is this:</p> <pre class="lang-MySQL prettyprint-override"><code>SELECT Readings.SampleID, Sample.BatchesID (case when location = '1' then AVG(voltage) else 0 end) avg_v_for_1, (case when location = '2' then AVG(voltage) else 0 end) avg_v_for_2, ... (case when location = '25' then AVG(voltage) else 0 end) avg_v_for_25 FROM DB.Readings INNER JOIN Sample ON Readings.SampleID = Sample.id WHERE Sample.BatchesID = 'specific_batch_id' GROUP BY Readings.location, Sample.id; </code></pre> <p>The problem is that this generates the following table:</p> <pre><code>SampleID avg_v_for_1 avg_v_for_2 ... avg_v_for_25 1 4.73 0 ... 0 1 0 4.76 ... 0 1 0 0 ... 6.73 2 3.87 0 ... 0 2 0 4.83 ... 0 ... </code></pre> <p>How can I get MySQL to gather ALL the average values for EVERY location on a SINGLE row? I have tried removing the group by location and only group by sampleID but then I only get the values for the first location and everything else becomes 0.</p> <p>Any help is appreciated, thank you!</p>
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    1. USMagneTism
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      1. VTUpMod
    1. COYour database structure is not making things easier. I suggest you normalize your database. First thing to do is have a separate *Locations* table that you can refer to for your locations.
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      1. USJan Doggen
    2. COI told the ones responsible for the structuring that but apparently "we don't have the resources to do that". I completely agree with you :)
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