稍微复杂的SQL查询

Question

编写一个SQL查询，按用户返回文章数量，如下列结果与列标题：＆＃39; user_id＆＃39;，＆＃39; username＆＃39;，＆＃39; total_count_of_articles＆＃39;按文章数量排序

Answer 1

这样的东西应该返回指定的结果集：

 SELECT u.id AS user_id
      , u.user_name
      , SUM(a.user_id IS NOT NULL) AS total_count_of_articles
   FROM users u
   LEFT
   JOIN users_articles a
     ON a.user_id = u.id
  GROUP BY u.id, u.user_name
  ORDER BY total_count_of_articles DESC