关联子查询

关联子查询 按照商品分类计算平均价格 select avg(p) from t group by a 按照商品种类对平均销售价格单价进行比较 select id,mei,tanka from t as a where tanka > (select AVG(tanka) from t as b where a.zl=b.zl group by zl) 关联名称的做用域：在子查询内部设定的关联名称，

>>阅读原文<<