title: What is the difference between `->>` and `->` in Postgres SQL?
body: <p>What is the difference between <code>-&gt;&gt;</code> and <code>-&gt;</code> in SQL?</p>
  
  <p>In this thread (<a href="https://stackoverflow.com/questions/19422233/check-if-field-exists-in-json-type-column-postgresql">Check if field exists in json type column postgresql</a>), the answerer basically recommends using,</p>
  
  <pre><code>json-&gt;'attribute' is not null
  </code></pre>
  
  <p>instead of,</p>
  
  <pre><code>json-&gt;&gt;'attribute' is not null
  </code></pre>
  
  <p>Why use a single arrow instead of a double arrow? In my limited experience, both do the same thing.</p>