日常开发中可能遇到很多分组的业务需求,比如分组查询后取第一条、组内排序等,除了用group by来做分组,我们还可以使用row_number() over(partition by)这个函数来解决分组问题。
简单总结下,并结合示例简单说下:
可适用需求:
(1)、某几个字段作为唯一键,删除其他数据
delete from student where id not in (
select t.id from (
select row_number() over (
partition by username,type
order by
id desc
) rn,
id,username,stu_code,source,type
from student
) t where t.rn = 1
)
(2)、分组查询取组内第一条数据或组内排序后取第一条数据
select t.id,t.username,t.stu_code,t.source,t.type from (
select row_number() over (
partition by username,type
order by
id desc
) rn,
id,username,stu_code,source,type
from student
) t where t.rn = 1
(3)、分组查询,每组数据全部展示
select row_number() over (
partition by username,type
order by
id desc
) rn,
id,username,stu_code,source,type
from student
注意:该函数在mysql中8.0版本以上才可生效!!!!!