mysql left join and count code example

Example 1: mysql select and count left join

select
  t.Topic,
  t.Title,
  count(distinct s.starID) as StarCount,
  count(distinct m.User) as UserCount,
  count(distinct m.messageID) as MessageCount
from
  Topics t
  left join Messages m ON m.Topic = t.Topic
  left join Stars_Given s ON s.Topic = t.Topic
group by
  t.Topic,
  t.Title

Example 2: use of where in left join in mysql

SELECT bk1.book_name,bk1.isbn_no,bk1.book_price,bk1.pub_lang         
FROM  book_mast bk1          
LEFT JOIN book_mast bk2 ON bk1.book_price<bk2.book_price        
WHERE bk2.pub_lang='German';