题解 | #列出供应商及其可供产品的数量#
列出供应商及其可供产品的数量
https://www.nowcoder.com/practice/17f22851cf204019b51a36761a3afc79
select v.vend_id, count(p.prod_id) as prod_id from Vendors v left join Products p on v.vend_id = p.vend_id group by v.vend_id order by v.vend_id;
使用左外连接，然后按vendors表的id分组，因为是以左表作为基准
