已采纳回答 / 天青烟雨色
物理外键指的是使用foreign key 作为外键关联另一张的字段的连接方法,而且限定了引擎为InnoDB,而逻辑外键,又叫做事实外键,是因为存在语法上的逻辑关联而产生的外键,需要有连接关键词inner join 或者left join 等等和连接部分,也就是on后面的部分,如果需要对应的设置,也可以加上set等语句
2017-05-26
为什么在查找所有分类及其子类的后面加上以p.type_name;分组显示异常啊
Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column 't1.s.type_name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
Expression #3 of SELECT list is not in GROUP BY clause and contains nonaggregated column 't1.s.type_name' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
2017-05-26