您可以加入并执行条件聚合：

select
    b.id,
    b.name
    max(case when tib.content = 'math book'  then 'Yes' else 'No' end) has_math,
    max(case when tib.content = 'SQL book'   then 'Yes' else 'No' end) has_sql,
    max(case when tib.content = 'comic book' then 'Yes' else 'No' end) has_comic
from bag b
inner join things_in_bag tib on tib.bag_id = b.id
group by b.id, b.name

可以使用条件聚合：

select bag_id,
       max(case when content = 'math book' then 'Yes' else 'No' end) as has_math_book,
       max(case when content = 'SQL book' then 'Yes' else 'No' end) as has_sql_book,
       max(case when content = 'comic book' then 'Yes' else 'No' end) as has_comic_book
from things_in_bag
group by bag_id;