5 ways to delete duplicate records Oracle
In Oracle there are many ways to delete duplicate records. Note that below example are described to just explain the different possibilities.
Consider the EMP table with below rows
create table emp(
EMPNNO integer,
EMPNAME varchar2(20),
SALARY number);
10 Bill 2000
11 Bill 2000
12 Mark 3000
12 Mark 3000
12 Mark 3000
13 Tom 4000
14 Tom 5000
15 Susan 5000
1. Using rowid
SQL > delete from emp
where rowid not in
(select max(rowid) from emp group by empno);
This technique can be applied to almost scenarios. Group by operation should be on the columns which identify the duplicates.
2. Using self-join
SQL > delete from emp e1
where rowid not in
(select max(rowid) from emp e2
where e1.empno = e2.empno );
3. Using row_number()
SQL > delete from emp where rowid in
(
select rid from
(
select rowid rid,
row_number() over(partition by empno order by empno) rn
from emp
)
where rn > 1
);
This is another efficient way to delete duplicates
4. Using dense_rank()
SQL > delete from emp where rowid in
(
select rid from
(
select rowid rid,
dense_rank() over(partition by empno order by rowid) rn
from emp
)
where rn > 1
);
Here you can use both rank() and dens_rank() since both will give unique records when order by rowid.
5. Using group by
Consider the EMP table with below rows
10 Bill 2000
11 Bill 2000
12 Mark 3000
13 Mark 3000
SQL > delete from emp where
(empno,empname,salary) in
(
select max(empno),empname,salary from emp
group by empname,salary
);
