case when decode

create table Course(
 id int primary key,
 name varchar(20),
 score varchar(20)
);

insert into Course values(1,'java','80');
insert into Course values(2,'oracle','70');
insert into Course values(3,'jsp','60');
insert into Course values(4,'javascript','40');
select * from Course;
drop table Course

select id,
       name,
       score,
       case
         when score > 60 then
          'Pass'
         else
          'Fail'
       end as status
  from Course
  
select id, name, score, decode(sign(score - 60), 1, 'pass', 'fail') status
  from Course;

create table tusers(
 id int primary key,
 code varchar(20),
 name varchar(20)
);
insert into tusers values(1,'ST-001','lee');
insert into tusers values(2,'ST-002','zhang');
insert into tusers values(3,'ST-003','wang');
insert into tusers values(4,'ST-002','zhang');
insert into tusers values(5,'ST-003','wang');
insert into tusers values(6,'ST-001','lee');
select * from tusers;

select * from tusers where id in(select min(id) id from tusers t group by t.code) 
drop table tusers;

create table tusers(
 id int primary key,
 name varchar(20)
);
create table tscores(
 id int primary key,
 score varchar(20)
);
insert into tusers values(1,'lee');
insert into tusers values(2,'zhang');
insert into tusers values(4,'wang');
delete from tusers t where t.id ='3'

insert into tscores values(1,'80');
insert into tscores values(2,'100');
insert into tscores values(3,'90');

select tusers.id 編號，tusers.name 名稱, tscores.score 分數
  from tusers
  inner join tscores
    on tusers.id = tscores.id

。。。。。