title: Restricting a column to accept only 2 values
body: <p>I have a column called "Patient Type" in a table. I want to make sure that only 2 values can be inserted in to the column , either opd or admitted, other than that, all other inputs are not valid. </p>
  
  <p>Below is an example of what I want</p>
  
  <p><img src="https://i.stack.imgur.com/ngTjY.png" alt="enter image description here"></p>
  
  <p>How do I make sure that the column only accepts "opd" or "admitted" as the data for "Patient Type" column.</p>