title: Multiple single field vs compound index
body: <p>what is the difference of create multiple single field index vs a compound index as follow</p>
  
  <pre><code>db.products.createIndex( { "item": 1 } )
  db.products.createIndex( { "stock": -1 } )
  </code></pre>
  
  <p>vs</p>
  
  <pre><code>db.products.createIndex( { "item": 1, "stock": -1 }
  </code></pre>
  
  <p>Also, after i create a compound index do i need to separately create a single field index for each <code>item</code>, <code>stock</code>? if yes, in what scenario do i need to do that?</p>