在做統計是很多情況會用到分組排序 結合談論的方法
自己建了乙個demo驗證 留在這裡以便備份
create table student2(
student_id number primary key,
student_name varchar2(30) not null)
create table score(
score_id number primary key,
student_id number,
course_id number,
score number)
create table course(
course_id number primary key,
course_name varchar2(30)) ;
insert into course values (1,'課程1');
insert into course values (2,'課程2');
insert into course values (3,'課程3');
insert into course values (4,'課程4');
insert into score values (1,1,1,90);
insert into score values (2,1,2,89);
insert into score values (3,1,3,88);
insert into score values (4,1,4,85);
insert into score values (5,2,1,86);
insert into score values (6,2,2,80);
insert into score values (7,2,3,56);
insert into score values (8,2,4,98);
insert into score values (9,3,1,67);
insert into score values (10,3,4,34);
insert into score values (11,3,2,67);
insert into score values (12,3,3,90);
insert into score values (13,4,1,91);
insert into score values (14,4,2,92);
insert into score values (15,4,3,93);
insert into score values (16,4,4,94);
insert into score values (17,5,1,98);
insert into score values (18,5,2,99);
insert into score values (45,5,3,98);
insert into score values (46,5,4,99);
insert into score values (19,6,1,88);
insert into score values (20,6,2,89);
insert into score values (21,6,3,88);
insert into score values (22,6,4,89);
insert into score values (23,7,1,78);
insert into score values (24,7,2,79);
insert into score values (25,7,3,78);
insert into score values (26,7,4,79);
insert into score values (27,8,1,71);
insert into score values (28,8,2,72);
insert into score values (29,8,3,73);
insert into score values (30,8,4,74);
insert into score values (31,9,1,61);
insert into score values (32,9,2,62);
insert into score values (33,9,3,63);
insert into score values (34,9,4,64);
insert into score values (35,10,1,55);
insert into score values (36,10,2,65);
insert into score values (37,10,3,53);
insert into score values (38,10,4,54);
insert into student2 values (1,'張1');
insert into student2 values (2,'張2');
insert into student2 values (3,'張3');
insert into student2 values (4,'張4');
insert into student2 values (5,'張5');
insert into student2 values (6,'張6');
insert into student2 values (7,'張7');
insert into student2 values (8,'張8');
insert into student2 values (9,'張9');
insert into student2 values (10,'張10');
用rank() dense_rank()具有並列名次之分
select *
from (select a.score,
b.student_name,
c.course_name,
rank() over(partition by a.course_id order by a.score desc) rk
from score a, student2 b, course c
where a.student_id = b.student_id
and a.course_id = c.course_id) ss
where ss.rk <= 4
而採用row_number()是直接去行數 不管是否具有相同資料
select *
from (select a.score,
b.student_name,
c.course_name,
row_number() over(partition by a.course_id order by a.score desc) rk
from score a, student2 b, course c
where a.student_id = b.student_id
and a.course_id = c.course_id) ss
where ss.rk <= 4
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