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POPopulate new column with values from database MySQL
 

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    <p>I've a MySQL query where I fetch with association a list of users' visits ordered by desc date.</p> <pre><code>SELECT `id`, `name`, `date` FROM `logs` WHERE `iid` = ? ORDER BY `date` DESC'; </code></pre> <p>Each log has <code>iid, id, name, date</code>, the generated array so has the 3 requested values for each row.</p> <p>Here an example of the database:</p> <pre><code>| iid | id | name | date | --------------------------------------------- | 1 | 1 | foo | 2013-09-13 10:14 | | 2 | 1 | foo | 2013-09-12 08:10 | | 2 | 1 | foo | 2013-09-11 14:43 | | 1 | 1 | foo | 2013-09-10 15:12 | </code></pre> <p><code>iid</code> is the page, <code>id</code> the user id.</p> <p>Now I need to add a 4th column, called <code>lastvisit</code> which should contain the date of the previous visit by each user on each <code>iid</code>.<br> So I should have two different <code>lastvisit</code> values for the two <code>iid</code>:</p> <pre><code>| iid | id | name | date | lastvisit | ----------------------------------------------------------------- | 1 | 1 | foo | 2013-09-13 10:14 | 2013-09-12 15:12 | | 2 | 1 | foo | 2013-09-12 08:10 | 2013-09-11 14:43 | | 2 | 1 | foo | 2013-09-11 14:43 | null | | 1 | 1 | foo | 2013-09-10 15:12 | null | </code></pre> <p>I will add this column to the database and at each visit I will check the most recent visit to get the <code>lastvisit</code> value to put in the new entry. </p> <p>My problem is about the already recored entries, which have not the value for <code>lastvisit</code>. </p> <p>I need to populate them with a query, something like:</p> <pre><code>UPDATE `logs` SET `lastvisit` = ( SELECT `date` FROM `logs` WHERE `id` = ? AND 'iid' = ? ORDER BY `date` DESC' LIMIT 0, 1; ) </code></pre> <p>Obviosly this query doesn't work, is it possible to write a query to perform this task for each entry?</p>
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