title: MySQL Determine longest VarChar length
body: <p>I am trying to optimize my database.  In order to do so, I need to be able to determine the longest data entry in a varchar column, and then trim the column definition to just above that.</p>
  
  <p>How can I find out, using sql, the length of the longest varchar entry in my table?</p>
  
  <pre><code>CREATE TABLE `poller_output` (
    `local_data_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
    `rrd_name` varchar(19) NOT NULL DEFAULT '',
    `time` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
    `output` varchar(200) NOT NULL DEFAULT '',
    PRIMARY KEY (`local_data_id`,`rrd_name`,`time`)
  ) ENGINE=MEMORY DEFAULT CHARSET=utf8
  </code></pre>