《mysql必知必会》学习_第13章_20180803_欢
第13章：分组过滤。P83select count(*) as num_prods from products where vend_id=1003; #返回vend_id=1003的产品数目总值#P84select count(*) as num_prods from products group by vend_id; #返回各个vend_id所提供的产品数量，不需要指定计...
