Listagg Overflow function implementation (Oracle SQL) - sql

Question

I am using LISTAGG function for my query, however, it returned an ORA-01489: result of string concatenation is too long error. So I googled that error and found out I can use ON OVERFLOW TRUNCATE and I implemented that into my SQL but now it generates missing right parenthesis error and I can't seem to figure out why?
My query
SELECT DISTINCT cust_id, acct_no, state, language_indicator, billing_system, market_code,
EMAIL_ADDR, DATE_OF_CHANGE, TO_CHAR(DATE_LOADED, 'DD-MM-YYYY') DATE_LOADED,
(SELECT LISTAGG( SUBSTR(mtn, 7, 4),'<br>' ON OVERFLOW TRUNCATE '***' )
WITHIN GROUP (ORDER BY cust_id || acct_no) mtnlist
FROM process.feature WHERE date_loaded BETWEEN TO_DATE('02-08-2018','MM-dd-yyyy')
AND TO_DATE('02-09-2018', 'MM-dd-yyyy') AND cust_id = ffsr.cust_id
AND acct_no = ffsr.acct_no AND filename = 'FEATURE.VB2B.201802090040'
GROUP BY cust_id||acct_no) mtnlist
FROM process.feature ffsr WHERE date_loaded BETWEEN TO_DATE('02-08-2018','MM-dd-yyyy')
AND TO_DATE('02-09-2018','MM-dd-yyyy') AND cust_id BETWEEN 0542185146 AND 0942025571
AND src_ind = 'B' AND filename = 'FEATURE.VB2B.201802090040'
AND letter_type = 'FA' ORDER BY cust_id;

Answer 1

With a little bit of help by XML, you might get it work. Example is based on HR schema.
SQL> select
2 listagg(s.department_name, ',') within group (order by null) result
3 from departments s, departments d;
from departments s, departments d
*
ERROR at line 3:
ORA-01489: result of string concatenation is too long
SQL>
SQL> select
2 rtrim(xmlagg(xmlelement (e, s.department_name || ',')).extract
3 ('//text()').getclobval(), ',') result
4 from departments s, departments d;
RESULT
--------------------------------------------------------------------------------
Administration,Administration,Administration,Administration,Administration,Admin
SQL>

Answer 2

This demo sourced from livesql.oracle.com
-- Create table with 93 strings of different lengths, plus one NULL string. Notice the only ASCII character not used is '!', so I will use it as a delimiter in LISTAGG.
create table strings as
with letters as (
select level num,
chr(ascii('!')+level) let
from dual
connect by level <= 126 - ascii('!')
union all
select 1, null from dual
)
select rpad(let,num,let) str from letters;
-- Note the use of LENGTHB to get the length in bytes, not characters.
select str,
sum(lengthb(str)+1) over(order by str rows unbounded preceding) - 1 cumul_lengthb,
sum(lengthb(str)+1) over() - 1 total_lengthb,
count(*) over() num_values
from strings
where str is not null;
-- This statement implements the ON OVERFLOW TRUNCATE WITH COUNT option of LISTAGG in 12.2. If there is no overflow, the result is the same as a normal LISTAGG.
select listagg(str, '!') within group(order by str) ||
case when max(total_lengthb) > 4000 then
'! ... (' || (max(num_values) - count(*)) || ')'
end str_list
from (
select str,
sum(lengthb(str)+1) over(order by str) - 1 cumul_lengthb,
sum(lengthb(str)+1) over() - 1 total_lengthb,
count(*) over() num_values
from strings
where str is not null
)
where total_lengthb <= 4000
or cumul_lengthb <= 4000 - length('! ... (' || num_values || ')');