title: User table structure for registration and login system with email
body: <p>I want to know what is best table structure and indexes for users table (login by email and password) for best performance.
  I don't want to use usernames.
  I want to login with unique index (for better performance) with user email.</p>
  
  <p>Maybe best performance will be unique index for email and password together.</p>
  
  <p>Problem is that I want to be email indexed as unique for faster login.
  But in this case bad user can prevent another user to register knowing his email.</p>
  
  <p>The only idea I could think of some sort of unique email and password hash in one unique column. But I want know how its done the best.</p>
  
  <p>Part of my user table index structure (DB is MySQL)</p>
  
  <pre><code>user_id   - PRIMARY
  email     - UNIQUE
  password
  verified   (after verify email)
  </code></pre>