group by 和 having区别
sql中的group by 和 having 用法解析 --sql中的group by 用法解析: -- Group By语句从英文的字面意义上理解就是“根据(by)一定的规则进行分组(Group)”。 --它的作用是通过一定的规则将一个数据集划分成若干个小的区域,然后针对若干个小区域进行数据处理。 --注意:group by 是先排序后分组; --举例子说明:如果要用到group by 一般用到的就是“每这个字” 例如说明现在有一个这样的表:每个部门有多少人 就要用到分组的技术 select DepartmentID as '部门名称', COUNT(*) as '个数' from BasicDepartment group by...
SQL中group by的用法
首先先贴两条sql,大家看看有啥区别 view plain select * from all_txt A where id=(SELECT id from all_txt view plain where A.key_value = key_value ORDER BY release_time DESC limit 1); view plain select * from (select *,max(release_time) as timea view plain from all_txt group by key_value order by release_time desc) a order by timea desc; 然后说明下表的重要字段为三个id,key_value,release_time 作用是取每个相同key_value中release_time最新的...