Flag duplicate characters in a string - oracle

Question

I'm using oracle apex and i'm trying to write a pl/sql statement that will flag duplicates in a string. For example the string 'P,T,P,C' has two occurrences of the letter 'P' so it should raise an error. After all my digging the closest I got to achieving this was by using REGEXP_LIKE, but my regular expression skills are sub par. If anyone can assist that would be much appreciated.
DECLARE
v_seccode varchar2(10) := 'P,T,P,C';
BEGIN
if regexp_like(v_seccode, '(P{2,}?|C{2,}?|W{2,}?|T{2,}?)') then
raise_application_error(-20001,'You can not have the same SEC code listed more than once!');
end if;
END;

Answer 1

If your apex version is relatively recent you have access to the APEX_STRING API. Here is some code using that API, using same logic #Littlefoot showed in the other answer:
DECLARE
l_arr1 apex_t_varchar2;
l_arr2 apex_t_varchar2;
BEGIN
-- convert string to array with "," delimiter
l_arr1 := apex_string.split(:P1_SECCODE,',');
l_arr2 := l_arr1;
-- remove dupes from l_arr2
l_arr2 := l_arr2 MULTISET UNION DISTINCT l_arr2;
IF l_arr2 != l_arr1 THEN
return 'You can not have the same SEC code listed more than once!';
END IF;
END;
/

Answer 2

As you're using Apex, I suggest you create a validation within it. Code you posted suggests that you'd want to handle that elsewhere (process? Database trigger?).
Presuming that page item name is P1_SECCODE, validation - a PL/SQL function that returns error text - might look like this (read comments within code):
declare
l_seccode varchar2(20);
begin
-- Split P1_SECCODE into rows, fetch distinct values and aggregate them back.
-- If P1_SECCODE = 'P,T,P,C' then the L_SECCODE = 'P,T,C'
select listagg(distinct regexp_substr(:P1_SECCODE, '[^,]+', 1, level), ',')
within group (order by null)
into l_seccode
from dual
connect by level <= regexp_count(:P1_SECCODE, ',') + 1;
-- Now compare whether P1_SECCODE has the same number of commas as L_SECCODE.
-- If not, it means that P1_SECCODE contained duplicates so - return an error message
if regexp_count(:P1_SECCODE, ',') <> regexp_count(l_seccode, ',') then
return 'You can not have the same SEC code listed more than once!';
end if;
end;
If your database version doesn't support distinct within listagg, then first fetch distinct values and then aggregate them:
declare
l_seccode varchar2(20);
begin
-- Split P1_SECCODE into rows, fetch distinct values and aggregate them back.
-- If P1_SECCODE = 'P,T,P,C' then the L_SECCODE = 'P,T,C'
with temp as
(select distinct regexp_substr(:P1_SECCODE, '[^,]+', 1, level), ',') val
from dual
connect by level <= regexp_count(:P1_SECCODE, ',') + 1
)
select listagg(val, ',') within group (order by null)
into l_seccode
from temp;
-- Now compare whether P1_SECCODE has the same number of commas as L_SECCODE.
-- If not, it means that P1_SECCODE contained duplicates so - return an error message
if regexp_count(:P1_SECCODE, ',') <> regexp_count(l_seccode, ',') then
return 'You can not have the same SEC code listed more than once!';
end if;
end;

Answer 3

Given that your string can only have 4 possible letters PCWT, you could just use LIKE expressions along with a regular query:
SELECT *
FROM yourTable
WHERE string NOT LIKE '%P%P%' AND
string NOT LIKE '%C%C%' AND
string NOT LIKE '%W%W%' AND
string NOT LIKE '%T%T%';