title: Why PRIMARY_KEY is not deleted permanently?
body: <p>If I have a table in database and a table with an <code>AUTO_INCREMENT</code> and <code>PRIMARY_KEY</code> column.</p>
  
  <p>Suppose there are total <em>5 rows in table.</em></p>
  
  <p><em>Now consider this scenario...</em></p>
  
  <p>I deleted the <code>5</code>th row.</p>
  
  <p>The next time I will <code>INSERT</code> a row, it will have the PRIMARY_KEY <code>6</code>.</p>
  
  <p>Why the keys of <em>deleted records</em> are not also deleted permanently?</p>
  
  <p>If those are kept to recognize that what record was stored against that key, how come we know that what record that was, because that is deleted.</p>