title: Delete unique index mssql
body: <p>I have a table having email as unique key constraint. I want to drop it, How it will possible?</p>
  
  <p>Tried : <code>DROP INDEX email_2 ON users;</code></p>
  
  <p>No luck </p>
  
  <pre><code>    An explicit `DROP INDEX` is not allowed on index 'users.email_2'. 
  It is being used for `UNIQUE KEY` constraint enforcement.
  </code></pre>