Problem with increment variable and stored procedure to check duplicates - mysql

Question

I have problem with my procedure. I have table oferty_in which contain fields (id, status, ..., id_om). I want procedure which check if exist rows with the same id_om.
If exist, delete rows where status = 'N' (N - new).
My procedure almost works, but i have problem with iterate in loop. Every time I run my procedure ,procedure delete a half of rows. I don't know where is problem...
DELIMITER //
CREATE PROCEDURE check_duplicates_oferty_in()
BEGIN
DECLARE n INT DEFAULT 0;
DECLARE i INT DEFAULT 0;
DECLARE v_id_del BIGINT;
SELECT count(*) INTO n FROM oferty_in where status_oferty = 'N';
SET i=0;
WHILE i<n DO
IF EXISTS (SELECT id_om FROM oferty_in group by id_om having count(*) >= 2 LIMIT i,1) THEN
SELECT id_om INTO v_id_del FROM oferty_in group by id_om having count(*) >= 2 LIMIT i,1;
DELETE from oferty_in where id_om = v_id_del and status_oferty = 'N';
END IF;
SET i=i+1;
END WHILE;
END
//
I try also:
IF EXISTS (SELECT id_om FROM oferty_in group by id_om having count(*) >= 2 LIMIT i,1) THEN
SELECT id_om INTO v_id_del FROM oferty_in group by id_om having count(*) >= 2 LIMIT i,1;
DELETE from oferty_in where id_om = v_id_del and status_oferty = 'N';
SET i=i+1;
ELSE
SET i=i+1;
END IF;
But it's the same.
Every time half of rows. I use counter 'i' and while loop to iterate row by row on rows in oferty_in when status = 'N'. Anyone have a idea what I did wrong? Thanks for help and time.

Answer 1

You seem to want to delete rows with status = 'N' when id_om is duplicated.
I want procedure which check if exist rows with the same id_om. If exist, delete rows where status = 'N' (N - new).
Non-working code doesn't generally help explain logic, so this is what I am going by.
You definitely do not need a looping construct for this, nor a cursor:
delete o
from oferty_in o join
(select o2.id_om
from oferty_in o2
group by o2.id_om
having count(*) > 1 and sum(status = 'N') > 0
) o2
on o.id_om = o2.id_om
where o.status = 'N';