title: meaning of a KEY in CREATE TABLE statment in mysql
body: <p>I am working with mysql .</p>
  
  <p>I have checked the CREATE table statement , and I saw there a KEY word</p>
  
  <pre><code>| pickupspc | CREATE TABLE `pickupspc` (
    `McId` int(11) NOT NULL,
    `Slot` int(11) NOT NULL,
    `FromTime` datetime NOT NULL,
    `ToTime` datetime NOT NULL,
    `Head` int(11) NOT NULL,
    `Nozzle` int(11) DEFAULT NULL,
    `FeederID` int(11) DEFAULT NULL,
    `CompName` varchar(64) DEFAULT NULL,
    `CompID` varchar(32) DEFAULT NULL,
    `PickUps` int(11) DEFAULT NULL,
    `Errors` int(11) DEFAULT NULL,
    `ErrorCode` varchar(32) DEFAULT NULL,
    KEY `ndx_PickupSPC` (`McId`,`Slot`,`FromTime`,`ToTime`,`Head`)
  ) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
  </code></pre>
  
  <p>But what is the meaning of it ?
  It's not like a PRIMARY KEY right ?</p>
  
  <p>Thanks .</p>