【2020090401】排名 rank over的用法
（1）rank over（order by 列名）------该函数只适用于oracle
例：
1 select sid, sname, rank() over (order by score) as srank from sc;
（2）rank over（partition by 列名，order by 列名）
例：
1 select name, age, score, rank() over (partition by age order by score decs) as rank_num from student;
（按年龄分组，组内按分数降序排名）
注：dense_rank() 连续排名
rank () 可不连续排名
1 -- 查询各科成绩前三名的记录 2 3 SELECT cid, sid, score, srank FROM 4 (SELECT *, dense_rank() over (PARTITION by cid ORDER BY score DESC) AS srank 5 FROM sc) 6 AS t 7 WHERE t.srank<=3;
