title: How to select rows from MySQL table only if count of rows matching index meets value?
body: <p>I want to return rows from a MySQL table only if the count of the number of rows matching an index meets a certain number.</p>
  
  <p>Here's the issue: I have a table of user reviews that are indexed by username. Therefore, I have many rows with different reviews all indexed by usernames. I am creating a search filter, so I need to return the usernames of people who have a certain number of reviews (ie. number of review rows in the table).</p>
  
  <p>How would I create a MySQL query that would pull only usernames of people say that have 4 reviews (4 table row entries)?</p>