域、工作组和家庭组之间有什么区别？

select 5种子句：where 条件查询group by 分组having 筛选order by 排序limit 限制结果条数---------------------group bygroup by 用于统计，一般和max min sum avg count配合使用max求最大min求最小sum求总和avg求平均count求总行数注意：sum是求总和，而count是求总行数。1.max取出本店商品中的shop_price最大值:seclect max(shop_price) from goods;取出每个栏目中的shop_price最大值:seclect cat_id,max(shop_price) from goods group by cat_id;2.min取出每个栏目中的shop_price最小值:seclect cat_id,min(shop_price) from goods group by cat_id;3.sum取出每个栏目中的shop_price总和:seclect cat_id,sum(shop_price) from goods group by cat_id;4.avg取出每个栏目中的shop_price平均值:seclect cat_id,avg(shop_price) from goods group by cat_id;5.count取出每个栏目中的商品种类:seclect cat_id,count(*) from goods group by cat_id;---------------------注意：要把列名当成变量名来看本店每个商品价格比市场价格低多少钱：seclect goods_name,market_price - shop_price from goods;查询每个栏目下面积压的货款：select cat_id,sum(shop_price * goods_number) from goods group by cat_id;查询每个栏目下面积压的货款，变量也可以用别名，as ，如(sum(shop_price * goods_number) as huokuan)：select cat_id,sum(shop_price * goods_number) as huokuan from goods group by cat_id;