数据库学习——数据分组

数据分组

SELECT category_id,COUNT(*) FROM product GROUP BY product.`category_id` 

按照category_id进行分组

过滤分组

SELECT category_id,COUNT(*) AS num FROM product GROUP BY product.`category_id` HAVING  num <= 3

使用having字句对分组后的数据进行条件筛选