Remove Duplicate Row Data - sql

Question

I need to remove duplicates from my table (user_info). I always want to remove the row with the id column that is lower of the two rows being returned from my select/having query below. Any ideas on how to write the delete statement to remove the duplicates (lower user_info.id column) from the results of my select/having query below? I'm using Oracle 11g.
user_info table structure:
id (unique primary key number 10 generated by sequence)
user_id (number 10)
first_name (varchar2)
last_name (varchar2)
data example:
id user_id
______ ___________
37265 1455
265798 1455
sql to show duplicates:
select user_id, count(*)
from user_info
group by user_id
HAVING count(*) > 1

Answer 1

You can use the following query:
DELETE
FROM user_info
WHERE id NOT IN
(SELECT MAX(id)
FROM user_info
GROUP BY user_id);
This query will delete all the duplicate rows except the user_id row with maximum id.
Here's a SQL Fiddle which demonstrates the delete.

Answer 2

Start with this to show you only the duplicates
Select user_id, count(*) NumRows, Min(Id) SmallestId, Max(Id) LargestId
From user_info
Group by user_id
HAVING count(*) > 1
This will show you the min and max for each user_id (with the same value for SmallestId and LargestId if there are no duplicates.
Select user_id, count(*) NumRows, Min(Id) SmallestId, Max(Id) LargestId
From user_info
Group by user_id
For a User, you want to keep the MaxId and Delete everything else. So you can write a DELETE statement to be
DELETE From user_info
Where Id Not IN
(
Select Max(Id)
From user_info
Group by user_id
)
This will get the

Answer 3

drop table test;
/
create table test
(
ids number,
user_id number
);
/
insert into test
values(37265,1455);
/
insert into test
values(265798,1455);
/
select * from test;
delete from test t
where t.ids < (select max(ids) from test t1 where T1.USER_ID= T.USER_ID)
This query employs the sub query to do the same !