解决sql 过滤重复数据记录的方法(Oracle)

create table table1 (id int, ip varchar(15), city char(20));
 
insert into table1  values(1, '127.0.0.1', '深圳') ;
insert into table1  values(2, '127.0.0.2', '广州') ;
insert into table1  values(3, '127.0.0.2', '广州') ;
insert into table1  values(4, '127.0.0.2', '广州') ;
insert into table1  values(5, '127.0.0.2', '北京') ;
insert into table1  values(6, '127.0.0.4', '上海') ;
insert into table1  values(7, '127.0.0.4', '上海') ;
insert into table1  values(8, '127.0.0.4', '上海') ;
insert into table1  values(9, '127.0.0.7', '未知');
 
-- 按字段IP查询 
select * from table1 where id in 
-- 检索重复ip的纪录 
(select min(id) from table1 where ip in 
-- 求重复ip的其中一个id 
(select ip from table1 group by ip having count(1) >= 1) 
-- 取出重复的
ip group by ip ) ;

1	1	127.0.0.1          深圳                
2	2	127.0.0.2          广州                
3	6	127.0.0.4	         上海                
4	9	127.0.0.7	         未知

create table table2 (id int, ip varchar(15), city char(20));
 
insert into table2 values( 1, '127.0.0.1', '深圳') ;
insert into table2 values( 2, '127.0.0.2', '广州') ;
insert into table2 values( 3, '127.0.0.2', '广州') ;
insert into table2 values( 4, '127.0.0.3', '北京') ;
insert into table2 values( 5, '127.0.0.3', '北京') ;
insert into table2 values( 6, '127.0.0.4', '上海') ;
insert into table2 values( 7, '127.0.0.4', '上海') ;
insert into table2 values( 8, '127.0.0.4', '上海') ;
insert into table2 values( 9, '127.0.0.7', '未知');

-- 按字段city查询 
select * from table1 where id in 
-- 检索重复city的纪录 
(select min(id) from table1 where city in 
-- 求重复city的其中一个id 
(select city from table1 group by city having count(1) >= 1) 
-- 取出重复的city 
group by city );

1	1	127.0.0.1         深圳                
2	2	127.0.0.2	         广州                
3	4	127.0.0.3	         北京                
4	6	127.0.0.4	         上海                
5	9	127.0.0.7         未知