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POHow do I speed up my MySQL query that gets an AVG of most recent transaction per user?
 

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  1. POHow do I speed up my MySQL query that gets an AVG of most recent transaction per user?
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    <p>I'm pretty sure my implementation for this solution is the least efficient (takes 2 seconds to complete when run over only 30,000 records). Is there a faster way?</p> <p>My MySQL query, followed by explanation below:</p> <pre><code>SELECT DATE(m.date) AS day, AVG(t.amount) AS amount FROM transactions s LEFT JOIN users m ON m.id = s.user_id WHERE #only consider the most recent transaction for each user s.id = ( SELECT id FROM transactions s2 WHERE s2.user_id = s.user_id AND s2.created_date = ( SELECT MAX(created_date) FROM transactions s3 WHERE s3.user_id = s.user_id ) ) GROUP BY day ORDER BY day; </code></pre> <p>Basically it's saying "show the average transaction amount per day, considering only each user's most recent transaction".</p> <p>I've already created an index on created_date.</p> <p>I don't want to just select the MAX(transaction.id) for user related transactions, because there's no guarantee that new transaction records added to the table are always for newer real world transactions.</p>
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