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POHow to return the closest time slots grouped by an entity, but just for one closest available day, not every available day?
 

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  1. POHow to return the closest time slots grouped by an entity, but just for one closest available day, not every available day?
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    <p>I have a table that stores available appointments for a teacher, hourly based, with total freedom to add unlimited slots per day per teacher (as long as slots don't overlap). Example simplified structure:</p> <pre><code>CREATE TABLE time_slots ( id int(10) unsigned NOT NULL AUTO_INCREMENT, teacher_id mediumint(8) unsigned NOT NULL, slot bigint(20) unsigned NOT NULL DEFAULT '0', ); </code></pre> <p>The <strong>slot</strong> column stores the timestamp of the slot.</p> <p>How can I show all available slots for the first closest available day for every teacher? Notice: show all time slots of a given day and can't show more than one day for the same teacher.</p> <h2>Example data:</h2> <p>PS: using datetime just to make things more readable.</p> <pre><code>+----+------------+------------------+ | id | teacher_id | slot | +----+------------+------------------+ | 1 | 1 | 2013-04-10 08:00 | | 2 | 1 | 2013-04-10 09:00 | | 3 | 1 | 2013-04-10 09:30 | | 4 | 1 | 2013-04-11 08:00 | | 5 | 1 | 2013-04-11 09:00 | | 6 | 1 | 2013-04-11 10:30 | | 7 | 2 | 2013-04-12 07:00 | | 8 | 2 | 2013-04-12 09:00 | | 9 | 2 | 2013-04-14 08:00 | +----+------------+------------------+ </code></pre> <h2>Expected result:</h2> <p>Assuming a search is made on: <strong>2013-04-10 08:30</strong>, the returned results have to be:</p> <pre><code>+----+------------+------------------+ | id | teacher_id | slot | +----+------------+------------------+ | 2 | 1 | 2013-04-10 09:00 | | 3 | 1 | 2013-04-10 09:30 | | 7 | 2 | 2013-04-12 07:00 | | 8 | 2 | 2013-04-12 09:00 | +----+------------+------------------+ </code></pre> <ol> <li>Don't show id 1 because it is already past 08:00 from day 10/Apr.</li> <li>Don't show id 4, 5, 6 because we found the closest available slots for teacher = 1 to be id's 2 and 3.</li> <li>Don't show id 9 because for teacher = 2 the closest available slots are the 7 and 8, so don't return another day.</li> </ol> <h2>What I tried</h2> <p>I'm failing hard to come with a query, I just came with this basic query, but it makes no assumptions on getting just the 1st available day, and of course it doesn't return all available slots in a given day. It just returns 1 slot per teacher:</p> <pre><code>SELECT id, teacher_id, FROM_UNIXTIME(slot) FROM time_slots WHERE slot &gt;= [Actual timestamp] GROUP BY DATE(FROM_UNIXTIME(slot)) ORDER BY slot, teacher_id ASC </code></pre> <p>Note: I'm using FROM_UNIXTIME here just for purposes of debugging, of course I'll optimise indexes, etc later.</p>
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