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    <p>This is primarily a temporary file that slows down your query. The word <code>temporary</code> in <code>EXPLAIN</code> means that every time you run this query MySQL server has to create a temporary table. While it's small, it is held in memory and thus is relatively fast. When it becomes large enough, it is moved to the disk and makes the query run really slow.</p> <p>When is temporary table used? It is well described in the <a href="http://dev.mysql.com/doc/refman/5.0/en/internal-temporary-tables.html" rel="nofollow">MySQL Reference Manual &ndash; Optimizing Database Structure</a>. In your case, it must be happening because you're ordering by field <code>timestamp</code> which is not included into the <code>GROUP BY</code> clause.</p> <p>Next, do you really need to group by all of these fields? Since you're grouping by primary key of <code>events</code> table, grouping by another <code>event</code>'s fields would have no sense. Try executing this query:</p> <pre><code>$scheduler-&gt;render_table("events LEFT JOIN tblfollowers ON events.id_user = tblfollowers.username WHERE events.status = 'active' AND tblfollowers.follower_id = '$test' OR events.id_user = '$test' GROUP BY events.event_id, events.timestamp ORDER BY events.timestamp DESC" , "event_id", "start_date, start_date, event_name, details"); </code></pre> <p><strong>EDIT:</strong> By the way, didn't you forget to put the parentheses around the condition? <code>AND</code> takes precedence over <code>OR</code>.</p> <pre><code>WHERE events.status ='active' AND (tblfollowers.follower_id='$test' OR events.id_user='$test') </code></pre> <p>That way it seems more logical to me. </p>
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    1. COok well none of this seems to be working so maybe i can explain what i am trying to accomplish with the query. These problems started when I added 1,500 followers to the table tblfollowers. I am trying to get all events posted by id_user 50 in events as well as any events that follower_id 50 follows in tblfollowers.
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    2. COit is in parenthesis in my original example.
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    3. COTry adding an `INDEX` on `timestamp` field - it is necessary to avoid temporary table. By the way, how long does the query run? 1593x17 rows mustn't be too much even for on-disk filesort...
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