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
左连接可以保留右表的null值
共同列要指明
select a.vend_id,count(prod_id) prod_id
from Vendors a left join Products s
on a.vend_id =s.vend_id
group by vend_id
order by vend_id
