mysql 联合查询

mysql 联合查询：
books里包含book_name, cate
books_sale里包含：book_name，sale_num，create_time
需要按cate查询总共的sale_num:

select sum(b.sale_num) from books a right join books_sale b on (a.book_name = b.book_name) where a.cate  = '人文' and b.create_time > "2021-03-00" and b.create_time < "2021-04-00";