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    <p>Try this query (but don't try it on production data, but rather on a copy of this data):</p> <pre><code>update tabb_after_update tabb, ( select t.*, ( SELECT min( visit_id ) FROM tabb_after_update t1 WHERE t1.user_id = t.user_id AND t1.time_of_visit &lt;= t.time_of_visit AND t1.time_of_visit &gt;= subtime( t.time_of_visit, '00:20' ) ) new_id from tabb_after_update t ) tabb1 SET tabb.visit_id = tabb1.new_id WHERE tabb.user_id = tabb1.user_id AND tabb.visit_id = tabb1.visit_id ; </code></pre> <p>SQLFiddle demo --> <a href="http://www.sqlfiddle.com/#!2/caa08/1" rel="nofollow">http://www.sqlfiddle.com/#!2/caa08/1</a></p> <p><br><br><br> ------ EDIT ----- <br><br> Another version that "joins gaps" into one group if gaps are &lt;= 20 minutes.<br> </p> <pre><code>set @last_uid = 0; set @last_tm = '00:00'; set @last_vid = 0; update tabb_after_update tabb, ( select t.* , case when @last_uid = user_id AND cast( @last_tm as time) &gt;= subtime( time_of_visit, '00:20' ) then if( (@last_tm := time_of_visit ), @last_vid, @last_vid ) else if( (@last_uid := user_id) + (@last_vid := visit_id ) + (@last_tm := time_of_visit ), @last_vid, @last_vid ) end new_id from tabb_after_update t order by user_id, time_of_visit ) tabb1 SET tabb.visit_id = tabb1.new_id WHERE tabb.user_id = tabb1.user_id AND tabb.visit_id = tabb1.visit_id ; </code></pre> <p>SQLFiddle demo --> <a href="http://www.sqlfiddle.com/#!9/39f03/1" rel="nofollow">http://www.sqlfiddle.com/#!9/39f03/1</a> <br>In this demo the user 1 has entries from 17:10 to 17:50 with "gaps" betwen records less than 20 minutes, and the query "combines" all these records into one group.</p>
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    1. POMysql: update to create group of visit entries separated by no more than maxmium minutes
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    1. POMysql: update to create group of visit entries separated by no more than maxmium minutes
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    1. COThanks! Close... but seems it misses this: Say a user's visit_id 1 is at 19:00, #2 at 19:10, and #3 at 19:25. That should be one group with visit_ids 1,1,1. This code will make the visit_ids 1,1,2. (To test, change the time of visit 12 in your fiddle to 19:08... in that case, the visit_id should be 5, but the code will make the visit_id 9). This is the problem that I also find trying to do sql only: to make all visits as one group as long as no gap between visits n and n+1 is greater than 20min, even if the gap between non-sequential gaps (n->n+2, n->n+3, etc) is greater than 20.
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    2. CO@kenji359 I've appended a modified version of the query.
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    3. COWow, very nice! I tried it on a copy of the full table, and it works beautifully :) Very clever coding, for real. And actually executes faster than I expected. Thanks @kordirko :)
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