title: What does the line " KEY `idx_pid` (`person_id`), " mean?
body: <p>I am new to mysql and am working on an online server (MYSQL version 5.1.69) and i have the following table</p>
  
  <pre><code>CREATE TABLE `person_info` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `person_id` int(11) NOT NULL,
    `info_type_id` int(11) NOT NULL,
    `info` text NOT NULL,
    `note` text,
    PRIMARY KEY (`id`),
    KEY `idx_pid` (`person_id`),
    KEY `person_info_info_type_id_exists` (`info_type_id`)
  )
  </code></pre>
  
  <p>Can someone explain to me what " KEY <code>idx_pid</code> (<code>person_id</code>)," does? </p>