PL/SQL query IN comma deliminated string

Question

I am developing an application in Oracle APEX. I have a string with user id\'s that is comma deliminated which looks like this,

45,4932,20,19

Answer 1

Please dont use: WHERE ','||to_char(:P5_USER_ID_LIST)||',' like '%,'||to_char(u.user_id)||',%' because you'll force a full table scan although with the users table you may not have that many so the impact will be low but against other tables in an enterprise environment this is a problem.

EDIT: I have put together a script to demonstrate the differences between the regex method and the wildcard like method. Not only is regex faster but it's also a lot more robust.

-- Create table
create table CSV_TEST
(
  NUM NUMBER not null,
  STR VARCHAR2(20)
);


create sequence csv_test_seq;

begin
  for j in 1..10 loop
    for i in 1..500000 loop
     insert into csv_test( num, str ) values ( csv_test_seq.nextval, to_char( csv_test_seq.nextval ));
    end loop;
    commit;
  end loop;
end;
/

-- Create/Recreate primary, unique and foreign key constraints 
alter table CSV_TEST
  add constraint CSV_TEST_PK primary key (NUM)
  using index ;
alter table CSV_TEST
  add constraint CSV_TEST_FK unique (STR)
  using index;

select sysdate from dual;
select *
from csv_test t
where t.num in ( Select Regexp_Substr('100001, 100002,   100003   ,      100004, 100005','[^,]+', 1, Level) From Dual
                 Connect By Regexp_Substr('100001, 100002,100003, 100004, 100005', '[^,]+', 1, Level) Is Not Null);
select sysdate from dual;

select *
from csv_test t
where ('%,' || '100001,100002,   100003,  100004  ,100005' || ',%') like '%,' || num || ',%';
select sysdate from dual;
select *
from csv_test t
where t.num in ( Select Regexp_Substr('100001, 100002,   100003   ,      100004, 100005','[^,]+', 1, Level) From Dual
                 Connect By Regexp_Substr('100001, 100002,100003, 100004, 100005', '[^,]+', 1, Level) Is Not Null);
select sysdate from dual;

select *
from csv_test t
where ('%,' || '100001,100002,   100003,  100004  ,100005' || ',%') like '%,' || num || ',%';
select sysdate from dual;

drop table csv_test;
drop sequence csv_test_seq;