title: Call to_json on multiple columns using Postgres
body: <p>Say I have the following table schema in Postgres:</p>
  
  <pre><code>CREATE TABLE users (id text, email text, phone_number text);
  </code></pre>
  
  <p>And I, for whatever reason, want to select the email and the phone number as JSON:</p>
  
  <pre><code>SELECT to_json(users.email, users.phone_number) AS user FROM users WHERE id=usr_123;
  </code></pre>
  
  <p>I get an error that looks like this:</p>
  
  <pre><code>function to_json(text, text) does not exist 
  
  No function matches the given name and argument types. You might need to add explicit type casts.
  </code></pre>
  
  <p>But this works just fine:</p>
  
  <pre><code>SELECT to_json(users.*) AS user FROM users WHERE id=usr_123;
  </code></pre>
  
  <p>How can I select just a few columns (not all of them) using a <code>to_json</code> call in Postgres?</p>