title: How to fix 'column is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause
body: <p>I am writing a simple program using a database I've created but I have run into an issue, I am trying to determine the highest occurring referrer ID while also displaying the customer information</p>
  <pre><code>SELECT TOP (3) referrer_id,
      COUNT(referrer_id) AS value_occurance,
      customer_id, 
      CONCAT(first_name, ' ', last_name) AS full_name
  FROM customer
  GROUP BY referrer_id
  ORDER BY value_occurance DESC
  </code></pre>
  <p>This is my query.</p>
  <blockquote>
  <p>Column 'customer.customer_id' is invalid in the select list because it
  is not contained in either an aggregate function or the GROUP BY
  clause.</p>
  </blockquote>
  <p>This is the error I am receiving.</p>