我的两个sql在Oralce中发现重复记录有什么区别？

Question

如果记录重复，我想删除并留下一条记录。在我的表中，t_id是一个主键，它是int类型和自动增量，id是序列号并且是varchar类型。 起初，我的sql是这样的，但它似乎僵局，并且运行很长时间，似乎永远不会停止。

delete from tbtest 
Where t_id Not In (
select max(t_id) from tbtest having count(id)>1 
group by id 
) 
and id in (
select id from tbtest group by id having count(id)>1 
) 
and create_time<to_timestamp('2016-02-25 11:26:52','yyyy-mm-dd hh24:mi:ss') 

所以我改变它到另一种方式，它运行得非常快？它们之间有什么区别？

delete from tbtest where t_id in (
select t_id from tbtest 
Where t_id Not In (
select max(t_id) from tbtest having count(id)>1 
group by id 
) 
and id in (
select id from tbtest group by id having count(id)>1 
) 
and create_time<=to_timestamp('2016-02-25 11:26:52','yyyy-mm-dd hh24:mi:ss') 
) 

Answer 1

这是一个概念验证。试试看看是否有帮助。

create table ta (t_id number primary key, id varchar2(10), val number); 

insert into ta 
    select 1, '1', 33 from dual union all 
    select 2, '2', 44 from dual union all 
    select 3, '2', 55 from dual; 

commit; 

select * from ta; 

     T_ID ID    VAL 
---------- ---------- ---------- 
     1 1     33 
     2 2     44 
     3 2     55 

delete from ta 
where t_id in (select t_id from (select t_id, id, 
     row_number() over (partition by id order by t_id desc) rn from ta) where rn > 1); 

1 row deleted. 

select * from ta; 

     T_ID ID    VAL 
---------- ---------- ---------- 
     1 1     33 
     3 2     55