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POCounting records of a table with multiple foreign keys (MySQL)
 

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    <p>I have a MySQL database with various tables whose records can be tagged, so I have a <code>tags</code> table, and a <code>tag_associations</code> table that relates tags to other "taggable" tables via multiple foreign keys, and also to an "owning" user -- my fields are something like the following:</p> <ul> <li>tag_association_id (primary key)</li> <li>user_id (tag association creator)</li> <li>tag_id (related tag)</li> <li>artist_id (tagged artist, can be null)</li> <li>album_id (tagged album, can be null)</li> <li>track_id (tagged track, can be null)</li> </ul> <p>I basically want to count all items that have been tagged a particular tag -- so something along the results of this query:</p> <pre><code>SELECT COUNT(ta.tag_association_id) AS how_many FROM tag_associations AS ta LEFT JOIN users AS u ON ta.user_id = u.user_id WHERE ta.tag_id = '480' AND u.user_status = 'active' </code></pre> <p>But the problem with this query lies in cases where the same tag has been applied to the same item by multiple users, so if 2 different users tag the artist 'Bobby Jones Band' as 'rad', it counts both of the tag associations where I just want to count it once. I tried adding this to the above:</p> <pre><code>GROUP BY ta.artist_id, ta.album_id, ta.track_id </code></pre> <p>...which got me close, but didn't yield the exact results I needed -- it gave me multiple row results of different counts. Is there any magic I can use in a case like this and keep it in a single query? While remaining as efficient as possible, of course :) Thanks!</p>
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    1. USChris Forrette
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