oracle sql 经典例子 班级科目排名 去重

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-------------------------------   经典成绩排名  ----------------------------------------
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-- drop table L_Class
create 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_Student
create 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;


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----------------------------    group by ... having ...    ---------------------------
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---  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;



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----------------------------    去除重复数据    -------------------------------------
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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);