SQL question challenge (Article views)

Link to github

DDL Scripts

CREATE TABLE article_views (
   date            timestamp,
   viewer_id       int,
   article_id      int,
   author_id       int
  );
  
  INSERT INTO article_views VALUES ('2017-08-01',123, 456 ,789);
  INSERT INTO article_views VALUES ('2017-08-02',432 ,543, 654);
  INSERT INTO article_views VALUES ('2017-08-01',789, 456 ,789);
  INSERT INTO article_views VALUES ('2017-08-03',567, 780, 432);
  INSERT INTO article_views VALUES ('2017-08-01',789, 457    ,789);
     
  date        viewer_id        article_id      author_id
  2017-08-01 123   456   789
  2017-08-02 432   543   654
  2017-08-01 789   456   789
  2017-08-03 567   780   432
  2017-08-01 789   457   789 

QUESTIONS
 1)HOW MANY ARTICLES AUTHORS HAVE NEVER VIEWED THEIR OWN ARTICLE?

select vw.viewer_id,au.author_id 
   from article_views vw left 
   outer join article_views au 
    on vw.viewer_id=vw.author_id 
   where au.author_id isnull;
   +-----------+-----------+
   | viewer_id | author_id |
   +-----------+-----------+
   |       123 |      NULL |
   |       432 |      NULL |
   |       567 |      NULL |
   +-----------+-----------+

2)HOW MANY MEMBERS VIEWED MORE THAN ONE ARTICLES ON 2017-08-01

select viewer_id 
  from article_views 
  where date =TIMESTAMP('2017-08-01') 
  group by viewer_id 
  having count(viewer_id) > 1;
   +-----------+
   | viewer_id |
   +-----------+
   |       789 |
   +-----------+