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POdistinct records based on the most recent version
 

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    <p>I list comments for an entry and I allow for user's to edit existing comments and it keeps track of those revisions.</p> <p>Table structure:</p> <p>comments: id, summary</p> <p>revisions: comment_id, revision_id, timestamp</p> <p>revisions.comment_id = comments.id</p> <p>revisions.revision_id = the id of the new comment, further explanation: when they select the existing comment, it will display an edit form and they may enter a new comment and submit it. It will insert it into the comments table as a new comment, grab the last id from that table and set it as revision_id in the revisions table.</p> <p>I want to do a select distinct on the revisions table (to retrieve multiple comment_id, revision_id into an array to be used within the application):</p> <p>for example: </p> <pre><code>select distinct comment_id from revisions </code></pre> <p>But is it possible to select the appropriate record based on the most recent comment (revisions.timestamp)?</p> <p>in theory:</p> <p>select distinct comment_id from revisions WHERE timestamp IS THE LARGEST</p> <p>revisions table example:</p> <pre><code>comment_id revision_id timestamp 2 12 20120222180000 2 13 20120222170000 5 18 20120222190000 5 19 20120222200000 </code></pre> <p>In this example of 4 rows, I'd want the query to return two rows,</p> <p>that being:</p> <p>comment_id = 2, revision_id = 12 timestamp = 20120222180000</p> <p>and</p> <p>comment_id = 5, revision_id = 19 timestamp = 20120222200000</p> <p>UPDATE: this seems to do the trick, but please let me know if there is a better way</p> <pre><code>SELECT distinct comment_id, max(timestamp) FROM revisions GROUP BY comment_id </code></pre> <p>UPDATE: I also need to include revision_id, the above query only includes comment_id and timestamp</p> <p>This did it:</p> <pre><code>SELECT distinct a.comment_id as comment_id, a.revision_id revision_id, a.timestamp as timestamp FROM REVISIONS a WHERE a.timestamp = ( SELECT max(b.timestamp) FROM revisions b WHERE b.comment_id = a.comment_id ) </code></pre>
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    1. COorder from largest and limit?
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      1. USAurimas Ličkus
    2. COI plan on having multiple revisions.comment_id stored into an array for later use. So retrieving only one row is not ideal in this situation.
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