---------------------------------------------------------------------------------------------------------------------- 经典成绩排名 --------------------------------------------------------------------------------------------------------------------------------- drop table L_Classcreate table L_Class(c_id varchar2(20) not null primary key,c_name varchar2(100),c_no varchar2(50) not null unique -- 班级编号);-- drop table L_Studentcreate table L_Student (s_id varchar2(20) not null primary key,s_no varchar2(50) not null unique, -- 学号s_name varchar2(100),c_no varchar2(50) not null -- 班级编号);-- drop table L_Score;create table L_Score(sc_id varchar2(20) not null primary key,sc_score number,sc_subject varchar2(50),s_no varchar2(50) not null -- 学号);-- 外键约束alter table L_Student add constraint Class_Student_FK foreign key (c_no) references L_Class (c_no); alter table L_Score add constraint Score_Student_FK foreign key (s_no) references L_Student (s_no); -----------------------insert into L_Class values('1','1班','c1');insert into L_Class values('2','2班','c2');insert into L_Class values('3','3班','c3');insert into L_Student values('1','s1','david1','c1');insert into L_Student values('2','s2','david2','c1');insert into L_Student values('3','s3','david3','c1');insert into L_Student values('4','s4','tom1','c2');insert into L_Student values('5','s5','tom2','c2');insert into L_Student values('6','s6','tom3','c2');insert into L_Student values('7','s7','kevin','c3');insert into L_Student values('8','s8','jerry','c3');insert into L_Student values('9','s9','fish','c3');insert into L_Student values('10','s10','peter','c3');insert into L_Score values('1','61','语文','s1');insert into L_Score values('2','62','语文','s2');insert into L_Score values('3','63','语文','s3');insert into L_Score values('4','64','语文','s4');insert into L_Score values('5','65','语文','s5');insert into L_Score values('6','66','语文','s6');insert into L_Score values('7','67','语文','s7');insert into L_Score values('8','68','语文','s8');insert into L_Score values('9','69','语文','s9');insert into L_Score values('10','70','语文','s10');insert into L_Score values('11','71','数学','s1');insert into L_Score values('12','72','数学','s2');insert into L_Score values('13','73','数学','s3');insert into L_Score values('14','74','数学','s4');insert into L_Score values('15','75','数学','s5');insert into L_Score values('16','76','数学','s6');insert into L_Score values('17','77','数学','s7');insert into L_Score values('18','78','数学','s8');insert into L_Score values('19','79','数学','s9');insert into L_Score values('20','80','数学','s10');select * from L_Student t;select t.* from L_Class t;select * from L_Score t;---- (全年级) 各科 成绩排名select * from ( select s.s_name 姓名, sc.sc_score 成绩, --row_number() 行号，没有并列第一 --dense_rank() 有并列第一，接下来就是第二， --rank() 有并列第一，接下来就是第三 dense_rank() over(partition by c.c_no, sc.sc_subject order by sc.sc_score desc) 排名, sc.sc_subject 科目, c.c_name 班级 from L_Class c, L_Student s, L_Score sc where c.c_no = s.c_no and s.s_no = sc.s_no --and c.c_name = '3班' --查询3班各科成绩排名 ) tmp where tmp.排名 <= 3 -- 前 3 名 --对结果集按照 班级、科目 排序 order by tmp.班级 desc, tmp.科目 desc, tmp.成绩 desc;----------------------------------------------------------------------------------------------------------------- group by ... having ... ------------------------------------------------------------------------------------------------------------------- 查询成绩表中成绩 >64 的记录，成绩分组select sc.sc_score from L_Score sc group by sc.sc_score having sc.sc_score > 75 order by sc.sc_score desc;----------------------------------------------------------------------------------------------------------------- 去除重复数据 --------------------------------------------------------------------------------------------------------------------------drop table L_User;create table L_User(u_id varchar2(20) not null primary key,u_name varchar2(100),u_age number);insert into L_User values('1','david',20);insert into L_User values('2','david',20);insert into L_User values('3','kevin',23);insert into L_User values('4','tom',25);insert into L_User values('5','kevin',30);insert into L_User values('6','kevin',20);select t.*,rowid,rownum from L_User t where rownum < 5;--- 去重( 去除名字相同的记录，保留一条 )delete from L_User u1 where u1.rowid < (select max(u2.rowid) from L_User u2 where u1.u_name=u2.u_name);--- 去重( 去除年龄相同的记录，保留一条 )delete from L_User u1 where u1.rowid < (select max(u2.rowid) from L_User u2 where u1.u_age=u2.u_age);--- 去重( 去除名字、年龄都相同的记录，保留一条 )delete from L_User u1 where u1.rowid < (select max(u2.rowid) from L_User u2 where u1.u_name=u2.u_name and u1.u_age=u2.u_age);?