title: How does Magento Install,Update scripts Actually work?
body: <p>I researched a lot for 5 hours.</p>
  
  <p>I actually referred the code given <strong><a href="https://magento.stackexchange.com/questions/65751/add-new-field-in-magento1-9-customer-registration">here</a></strong> to add new attribute to magento database for <strong>Customer</strong>.</p>
  
  <p>For that I initially used <code>install-1.0.0</code> script. But i needed some other fields to add to database so I created update script <code>upgrade-1.0.0-1.0.1</code> and added <code>&lt;version&gt;1.0.1&lt;/version&gt;</code> to my own extension "  <code>StackExchange_Customer/etc/StackExchange_Customer.xml</code></p>
  
  <p>But still the fields are not getting added in DB.</p>
  
  <p>There is no clear guide regarding </p>
  
  <ol>
  <li><p>How <code>Install script works</code> ,  <code>Update script works</code>??</p></li>
  <li><p>Which call goes into which file ??</p></li>
  <li><p>When actually Update, Install module get called ?</p></li>
  <li><p>Does it get called when I enable/disable module ? Or anything else ?</p>
  
  <p>Magento is already complex, without proper documentation on net ,
  stackoverflow , it has become even more complicated.</p></li>
  </ol>
  
  <p>Thanks.</p>