MySQLで四半期ごとの結果を取得するために日付フィールドをグループ化するにはどうすればよいですか？

これでうまくいくと思います：

SELECT YEAR(leaddate) AS year, QUARTER(leaddate) AS quarter, COUNT(jobid) AS jobcount
  FROM jobs
 WHERE contactid = '19249'
 GROUP BY YEAR(leaddate), QUARTER(leaddate)
 ORDER BY YEAR(leaddate), QUARTER(leaddate)