Deleting duplicate records based on two columns concatenation values - plsql

Question

I have a table employee has 30000 records. I need to delete duplicate records based on two columns concatenation. For example name and job, like
martin clerk
martin clerk
Below is my code:
declare
type typ_emp is table of emp%rowtype;
v_emp typ_emp;
cursor cur_emp
is
select *
from emp a
where rowid >
(select min (rowid)
from emp b
where concat (concat (b.ename, '-'), b.job) =
concat (concat (a.ename, '-'), a.job)
)
;
begin
open cur_emp;
loop
fetch cur_emp bulk collect into v_emp;
exit when v_emp.count = 0;
if v_emp.count > 0
then
for i in v_emp.first .. v_emp.last
loop
insert into backup_emp (ename, job)
values (v_emp (i).ename, v_emp (i).job)
;
end loop;
end if;
end loop;
close cur_emp;
delete
from emp s
where s.rowid >
any (select t.rowid
from emp t
where concat (concat (t.ename, '-'), t.job) =
concat (concat (s.ename, '-'), s.job));
commit;
exception
when others then
Raise;
end;
It is taking a long time to delete the records. Can anyone help me in tuning a query for this or suggest me what is the better approach.
Thanks in advance.

Answer 1

Creating function based index might improve your performance
CREATE INDEX concatindex ON emp (ename||'-'||job);
Delete statement would look like this
delete emp a where a.rowid > (select min(rowid) from emp b where b.ename||'-'||b.job=a.ename||'-'||a.job)
unless you need to insert deleted rows into backup table which is not clear from your question. If so I would rather bulkcollect rows into collection. Leave a comment if you need to have detailed this option.

Answer 2

I hope this helps.
SELECT ROWID, ename || '-' || job AS concatenation,
decode(rank() over(PARTITION BY ename || '-' || job ORDER BY ROWID), 1, 'keep', 'delete') AS to_do
FROM emp
ORDER BY ename || '-' || job, ROWID;

Answer 3

Here is my code changes:
cursor cur_emp
is
select *
from
(select b.*
,row_number()over(partition by concat (concat (b.ename, '-'), b.job) order by ename)cnt
from emp b
) where cnt>1;