title: Adding and updating a new dynamo db attribute in production environment
body: <p>I'm new to dynamo DB and wanted to understand how a new attribute can be added to an existing table.</p>
  <p>What is the best way to add a new attribute to an existing table in production and then update the items for that attribute based on some conditions? I'm thinking of doing this operation from a script</p>
  <p>For example:
  I've a dynamo db table <strong>Employee</strong> and it currently has a column <strong>Salary</strong> in the production environment. The requirement is to add a new column called <strong>Grade</strong> and update it's values based on the <strong>Salary</strong>. How to achieve this in an efficient way with any external scripts?</p>
  <p>I've tried it using <code>aws dynamodb update-item</code> but the issue is I don't know the key for it.</p>