title: How i can add not null field into an existing table, where as existing table contains a number of records
body: <ol>
  <li>I have an existing Db table (PostgreSQL) with the number records.</li>
  <li>I need to add a new column with NOT NULL constraints using Laravel migrations.</li>
  </ol>
  <p>Note: I don't want to lose my existing table data.</p>