SQL基础

Question

select author,book_name from table group by author having count(book_name)>=2

Answer 1

select author,book_name from table group by author,book_name having count(book_name)>=2

Answer 2

select author from table group by author having count(distinct book_name)>=2

Answer 3

select author from table group by author having count(book_name)>1

Answer 4

select author, book_name from table 
group by author, book_name
having count(*) > 1;