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POMySQL Subquery Count Using DATE_FORMAT alias
 

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    <p>I've been banging my head against the wall for the past hours trying to get this single query to work but having no success.</p> <p>I have a single table called viewer_log.</p> <p>Each row is a pageview with a session_id and timestamp attached to it.</p> <p>I am having troubles formatting the timestamp to a day, grouping by that day, but then counting the number of UNIQUE sessions per day.</p> <p>So far, for that query (which also took a long time to get working) is:</p> <pre><code>SELECT day, COUNT(*) as unique_sessions from (SELECT COUNT(viewer_session_id) AS sessions, DATE_FORMAT(timestamp, "%Y-%m-%d") AS day FROM viewer_log GROUP BY `viewer_session_id` HAVING day='2011-03-23') AS sessions; </code></pre> <p>You will notice the day is hardcoded, giving</p> <pre><code>mysql&gt; SELECT day, COUNT(*) as unique_sessions from (SELECT COUNT(viewer_session_id) AS sessions, DATE_FORMAT(timestamp, "%Y-%m-%d") AS day FROM viewer_log GROUP BY `viewer_session_id` HAVING day='2011-03-23') AS sessions; +------------+-----------------+ | day | unique_sessions | +------------+-----------------+ | 2011-03-23 | 21 | +------------+-----------------+ </code></pre> <p>I would like to expand these results without having to specify the day, which is where I am running into problems and not able to find an answer on the internet... I'm sure it's out there, not sure what I'm looking for.</p> <p>EG:</p> <pre><code>+------------+-----------------+ | day | unique_sessions | +------------+-----------------+ | 2011-03-21 | 14 | | 2011-03-22 | 11 | | 2011-03-23 | 21 | +------------+-----------------+ </code></pre> <p>I am having lots of trouble moving past this point, I have tried joining the table with a copy of its self but usually run into an unknown column name OR the results I THINK should be showing up are wrong:</p> <pre><code>mysql&gt; select DATE_FORMAT(v.timestamp, "%Y-%m-%d") AS date, count(sessions) as rows from (SELECT COUNT(viewer_session_id) AS sessions, DATE_FORMAT(timestamp, "%Y-%m-%d") AS date FROM viewer_log GROUP BY viewer_session_id) AS s JOIN viewer_log v ON (s.date=date) GROUP BY date; +------------+--------+ | date | rows | +------------+--------+ | 0000-00-00 | 2551 | | 0000-00-00 | 20408 | | 0000-00-00 | 20408 | | 0000-00-00 | 5102 | | 0000-00-00 | 2551 | | 0000-00-00 | 2551 | | 0000-00-00 | 63775 | | 0000-00-00 | 211733 | | 0000-00-00 | 53571 | | 0000-00-00 | 53571 | | 0000-00-00 | 53571 | | 0000-00-00 | 51020 | | 0000-00-00 | 48469 | | 0000-00-00 | 91836 | | 0000-00-00 | 86734 | | 0000-00-00 | 33163 | | 0000-00-00 | 45918 | | 0000-00-00 | 28061 | | 0000-00-00 | 86734 | | 0000-00-00 | 76530 | | 0000-00-00 | 53571 | | 0000-00-00 | 33163 | +------------+--------+ 22 rows in set, 1 warning (0.63 sec) </code></pre>
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