title: MySQL Number in KEY parameter creation
body: <p>I looked and some SQL scripts and wondered what the number in the braces behind the KEY operator means?</p>
  
  <p>I provided a truncated sample of the script (from Wordpress), where you can see this in the 4th line.</p>
  
  <pre><code>CREATE TABLE IF NOT EXISTS `wp_usermeta` (
    `umeta_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (`umeta_id`),
    KEY `meta_key` (`meta_key`(191))
  ) ENGINE=InnoDB;
  </code></pre>