text: // Hi, I'm Yanzhan. I'm interested in all kinds of algorithmic problems. Also, I'm fascinated with javascript. If you want to learn more about programming problems and javascript, please visit my Youtube Channel (https://www.youtube.com/channel/UCDkz-__gl3frqLexukpG0DA?view_as=subscriber), Twitter Account (https://twitter.com/YangYanzhan), GitHub Repo (https://github.com/yangyanzhan/code-camp) or HomePage (https://yanzhan.site/).
  
  // 开始分析
  // 1. SQL。
  // 结束分析
  
  // 开始编码
  
  select
      s.seller_name
  from
      seller s
  where
      not exists(
          select
              distinct o.seller_id
          from
              orders o
          where
              year(o.sale_date) = '2020'
              and o.seller_id = s.seller_id
      )
  order by
      s.seller_name asc;
  