初探oracle删除重复记录，只保留rowid最小的记录

create table my_users(
    id number,
    username varchar2(20),
    sal number
)

begin
    for i in  1..10 loop
        insert into  my_users values(i,‘carl_zhang‘,i+10);
    end loop;
end;

begin
    for i in  1..10 loop
        insert into  my_users values(i,‘carl_zhang‘,i+20);
    end loop;
end;

insert into my_users values(100,‘carl‘,20.3);

commit;

select rowid,rownum,a.* from my_users a
where 1=1
and exists(
    select ‘exist‘ from my_users b
    where 1=1
    and a.id=b.id
    and a.username=b.username
    having count(*)>1    
)
order by rowid

select rowid,rownum,a.* from my_users a
where 1=1
and exists(
    select ‘exist‘ from my_users b
    where 1=1
    and a.id=b.id
    and a.username=b.username
   -- having count(*)>1
    having count(*)>1 and a.rowid=max(b.rowid)
)
order by rowid

delete  from my_users a
where 1=1
and exists(
    select ‘exist‘ from my_users b
    where 1=1
    and a.id=b.id
    and a.username=b.username
   -- having count(*)>1
    having count(*)>1 and a.rowid=max(b.rowid)
)

select rowid,rownum,a.* from my_users a
where 1=1
and (a.id,a.username) in(
    select b.id,b.username from my_users b
    where 1=1  
    having count(*)>1
    group by  b.id,b.username    
)
order by rowid

select rowid,rownum,a.* from my_users a
where 1=1
and (a.id,a.username,rowid) in(
    select b.id,b.username,max(rowid) from my_users b
    where 1=1  
    having count(*)>1
    group by  b.id,b.username    
)
order by rowid

delete from my_users a
where 1=1
and (a.id,a.username,rowid) in(
    select b.id,b.username,max(rowid) from my_users b
    where 1=1  
    having count(*)>1
    group by  b.id,b.username    
)