title: Count rows with a specific condition in aggregate query
body: <p>I have this query to get the number of <code>PlayerSession</code>s with <code>reconnect = TRUE</code>, grouped by <code>Player.country</code>:</p>
  
  <pre><code>SELECT
      country,
      COUNT(*) AS with_reconnect
  FROM PlayerSession S LEFT JOIN Player P ON (P.id = S.player_id)
  WHERE reconnect = TRUE
  GROUP BY country
  </code></pre>
  
  <p>I'd like to modify it to show not just the reconnected session count, but also the total count, something like:</p>
  
  <pre><code>SELECT
      country,
      COUNT(*) AS total,
      (COUNT WHERE reconnect = TRUE) AS with_reconnect
  FROM PlayerSession S LEFT JOIN Player P ON (P.id = S.player_id)
  GROUP BY country
  </code></pre>
  
  <p>Is this possible, and if so, what is the proper syntax?</p>