稍微复杂的 SQL 查询

Question

编写一个 SQL 查询，按用户返回文章数，结果如下，列标题为：'user_id', 'username', 'total_count_of_articles' 按文章数排序

Answer 1

这样的事情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