【经典SQL】按照评论最多排序文章

comment表存了每个农场下的评论，实现按照评论最多排序农场。

关键点：多表查询（非连接查询）

    SELECT
        *
    FROM
        farm_info
    JOIN
        system_user
            ON farm_info.admin_id = system_user.admin_id,
             (select
            farm_id,
            count(*) as comment_num 
        from
            comment 
        group by
            farm_id) farm_comment
    WHERE
        farm_comment.farm_id = farm_info.farm_id 
    ORDER BY
        comment_num
                DESC

结果：