how to get better performance stored procedure oracle - oracle

Question

I wrote a stored procedure, but I don't think it is performing at all. How can I make it work better? Thanks.
Table A has 800k records. Table B has 36k records. Is test data, there will be more records in production environment.
Table B has customer_no column index defined.
I ran it once and it took 22 minutes.
create or replace procedure SP_KVKK
is
TYPE json_data_type IS RECORD
(
del_data CLOB
);
customer_no number(10);
r_del_data C%ROWTYPE;
l_deleted_cur SYS_REFCURSOR;
l_deleted_rec json_data_type;
l_sel_sql VARCHAR2 (500);
cursor mbb_list is
select customer_no from A;
begin
open mbb_list;
loop
fetch mbb_list into customer_no;
exit when mbb_list%notfound;
l_sel_sql := 'SELECT JSON_OBJECT(* RETURNING CLOB) AS DEL_DATA
FROM B where customer_no=' || customer_no;
open l_deleted_cur for l_sel_sql;
loop
fetch l_deleted_cur into l_deleted_rec;
exit when l_deleted_cur%notfound;
r_del_data.DELETED_DOCUMENT_JSON := l_deleted_rec.del_data;
r_del_data.DELETE_DATE := SYSTIMESTAMP;
Insert into C
values r_del_data;
end loop;
close l_deleted_cur;
end loop;
close mbb_list;
end;

Answer 1

The best thing you can do is deal with this construct as a single SQL statement. Stop thinking in terms of row-by-row nested loops which will always be slow, and look to SQL batch operations to handle this:
begin
-- insert your two columns into table C using the data
-- from table B returned as a json_object and systimestamp,
-- where only records from table B that have a customer_no
-- from table A will be selected
insert into C (deleted_document_json, delete_date)
select json_object(B.* returning clob), systimestamp
from B
inner join A using (customer_no);
commit;
end;