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Displaying posts with tag: duplicate (reset)
The small improvements of MySQL 5.6: Duplicate Index Detection

Here at the MySQL Performance Blog, we’ve been discussing the several new features that MySQL 5.6 brought: GTID-based replication, InnoDB Fulltext, Memcached integration, a more complete performance schema, online DDL and …

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Adding a Unique Constraint on a Table with Duplicate Data

After I moved back to Europe and Malta in order to set up our operations here, I was approached by a old friend of mine who wanted to know how to add a UNIQUE constraint and remove duplicates on a table, while keeping the newest records. He had been trying with ALTER TABLE but ran into problems as the older values were taken.

So, to help him out, I first solved it based on his original idea, and then figured I would post a small note about the solution here.

So, let’s say we have the following structure . . .

sql01 blogs> SHOW CREATE TABLE post1164\G
*************************** 1. row ***************************
       Table: post1164
Create Table: CREATE TABLE `post1164` (
  `a` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `b` varchar(5) DEFAULT NULL,
  `c` varchar(5) DEFAULT NULL,
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