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POSQL: How to Count occurrences in TableA, join with TableB and then order by occurences?
 

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  1. POSQL: How to Count occurrences in TableA, join with TableB and then order by occurences?
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    <h3>What I want:</h3> <p>For every User that is connected to Group_ID=1 I want to count the amount of activities this User have attended, and use that info to order by User with the most attendings DESC(ending).</p> <p><em>A table that connects Users to Groups:</em></p> <pre><code>user_r_group: ID User_ID Group_ID 1 1 1 2 3 1 3 2 1 4 1 2 &lt;-- User 1 connected to another group </code></pre> <p><em>A table that shows which activities User have attended:</em></p> <pre><code>activities_attended: ID Activity_ID User_ID 1 1 1 &lt;-- User 1 have attended 3 activities 2 1 3 3 1 2 4 2 1 &lt;-- User 1 have attended 3 activities 5 2 3 6 3 1 &lt;-- User 1 have attended 3 activities </code></pre> <p><strong>The outcome I'm looking for:</strong></p> <pre><code>User_ID Attendings 1 3 3 2 2 1 </code></pre> <h1>Is there a way to write a mysql_query to achieve this?</h1> <p>It sure feels like it. Or will I need to puzzle myself with loops in php with querycombinations?</p> <p>I've checked out ways to <a href="https://stackoverflow.com/q/10060325/2808954">join tables</a>, and I'm slightly familiar with <a href="https://stackoverflow.com/q/2283305/2808954">ORDER BY</a>, but I have no real clue how to store the attendings-info for every User and then order by it, to then put it all together in a query as wanted ;/ A lil help please?</p> <hr> <p><em>Solved it!</em></p> <p>Thanks to <a href="https://stackoverflow.com/users/477127/gordonm">GordonM</a> for guidance on where to look, and thanks to <a href="https://stackoverflow.com/users/1793906/milen-pavlov">Milen Pavlov</a> as well as <a href="https://stackoverflow.com/users/1445460/kirill-fuchs">Kirill Fuchs</a> for the code-samples. I combined the codes into my own prefered version. Kirill's code was however accurate on exception that he forgot the 'ORDER BY Attendings DESC' in the end ;)</p> <pre><code>SELECT COUNT(aa.User_ID) as Attendings, urg.User_ID FROM activities_attended aa INNER JOIN user_r_group urg ON urg.User_ID=aa.User_ID WHERE urg.Group_ID=1 GROUP BY urg.User_ID ORDER BY Attendings DESC </code></pre>
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    1. COYes, there is. It involves a join and an aggregate function, hopefully that's more than enough info for you to find what you're looking for
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    2. COAnd don't use `mysql_*` functions as they're error-prone and deprecated. Either use `mysqli_*` or even better: [PDO](http://php.net/manual/en/book.pdo.php)
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    3. CO@GordonM, found it! Thx. Combined some answers here to get what I wanted(Kirills at ~95% accuracy code-wise), will post my own answer to it with exact working result as well as recognition to involved parts. (Just waiting for 10+ rep or 8hours-limit for new users -.-)
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