Inserting into a table using a procedure only if the record doesn't exist yet - oracle

Question

I have a table that i'm trying to populate via a plsql script (runs on plsql developer). The actual DML statement
is contained in a procedure inside a package. The procedure only inserts if the record doesn't exist yet.
It doesn't work. The part that checks for existence returns true after the first iteration of the script loop even if it doesn't actually exist in the table.
If i put the commit outside of the loop, nothing gets inserted at all and the existence checks return true for all iteration even if the table it empty.
When i try to simplify the insert with existence check to be in just one statement without the exception handling, i get the same outcome.
Please tell me what I'm doing wrong here.
CREATE OR REPLACE PACKAGE BODY some_package
IS
PROCEDURE add_to_queue(id IN NUMBER)
IS
pending_record VARCHAR2(1);
BEGIN
-- this part succeeds even if nothing matches the criteria
-- during the loop in the outside script
SELECT 'Y'
INTO pending_record
FROM dual
WHERE EXISTS (SELECT 'x' FROM some_queue smq
WHERE smq.id = id AND smq.status IS NULL);
EXCEPTION
WHEN NO_DATA_FOUND THEN
INSERT INTO some_queue (seqno, id, activity_date)
VALUES (some_sequence.nextval, id, SYSDATE);
WHEN OTHERS THEN
NULL;
END;
END some_package;
CREATE TABLE some_queue
(
seqno VARCHAR2(500) NOT NULL,
id NUMBER NOT NULL,
activity_date DATE NOT NULL,
status VARCHAR2(25),
CONSTRAINT some_queue_pk PRIMARY KEY (seqno)
);
-- script to randomly fill in the table with ids from another table
declare
type ids_coll_tt is table of number index by pls_integer;
ids_coll_table ids_coll_tt;
cursor ids_coll_cur is
select tab.id
from (select *
from ids_source_table
order by dbms_random.value ) tab
where rownum < 10;
begin
open ids_coll_cur;
fetch ids_coll_cur bulk collect into ids_coll_table;
close ids_coll_cur;
for x in 1..ids_coll_table.count
loop
some_package.add_to_queue(ids_coll_table(x));
commit; -- if this is here, the first iteration gets inserted
end loop;
-- commit; -- if the commit is done here, nothing gets inserted
end;
Note: I translated this code to be more generic for posting. Forgive me if there are any typos.
Update: even if i put everything inside the script and not use the package, i'm not able to properly check for existence and I get the same results.

Answer 1

I figured out the solution:
CREATE OR REPLACE PACKAGE BODY some_package
IS
PROCEDURE add_to_queue(p_id IN NUMBER)
IS
pending_record VARCHAR2(1);
BEGIN
-- this part succeeds even if nothing matches the criteria
-- during the loop in the outside script
SELECT 'Y'
INTO pending_record
FROM dual
WHERE EXISTS (SELECT 'x' FROM some_queue smq
WHERE smq.id = p_id AND smq.status IS NULL);
EXCEPTION
WHEN NO_DATA_FOUND THEN
INSERT INTO some_queue (seqno, id, activity_date)
VALUES (some_sequence.nextval, p_id, SYSDATE);
WHEN OTHERS THEN
NULL;
END;
END some_package;
changing the parameter name fixed it. I guess the compiler gets confused if it's the same name as the table field.

Answer 2

Don't name the parameter the same as the column (use a prefix like p_ or in_) and you can do it in a single statement if you use a MERGE statement self-joining on the ROWID pseudo-column:
CREATE OR REPLACE PACKAGE BODY some_package
IS
PROCEDURE add_to_queue(
in_id IN NUMBER
)
IS
BEGIN
MERGE INTO some_queue dst
USING ( SELECT ROWID AS rid
FROM some_queue
WHERE id = in_id
AND status IS NULL ) src
ON ( src.rid = dst.ROWID )
WHEN NOT MATCHED THEN
INSERT (seqno, id, activity_date)
VALUES (some_sequence.nextval, in_id, SYSDATE);
END;
END some_package;