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POMySQL: updating a row and deleting the original in case it becomes a duplicate
 

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  1. POMySQL: updating a row and deleting the original in case it becomes a duplicate
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    <p>I have a simple <code>table</code> made up of two columns: <code>col_A</code> and <code>col_B</code>.</p> <p><strong>The primary key is defined over both.</strong></p> <p>I need to update some rows and assign to <code>col_A</code> values that may generate duplicates, for example:</p> <pre><code>UPDATE `table` SET `col_A` = 66 WHERE `col_A` = 70 </code></pre> <p>This statement sometimes yields a duplicate key error.</p> <p>I don't want to simply ignore the error with <code>UPDATE IGNORE</code>, because then the rows that generate the error would remain unchanged. Instead, <strong>I want them to be deleted when they would conflict with another row after they have been updated</strong></p> <p>I'd like to write something like:</p> <pre><code>UPDATE `table` SET `col_A` = 66 WHERE `col_A` = 70 ON DUPLICATE KEY REPLACE </code></pre> <p>which unfortunately isn't legal in SQL, so I need help finding another way around. Also, I'm using PHP and could consider a hybrid solution (i.e. part query part php code), but keep in mind that I have to perform this updating operation many millions of times.</p> <p>thanks for your attention,</p> <p>Silvio</p> <p>Reminder: <code>UPDATE</code>'s syntax has problems with joins with the same table that is being updated</p> <p><strong>EDIT</strong>: sorry, the column name in the WHERE clause was wrong, now I fixed it</p>
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