Oracle LISTAGG case return distinct values

Question

I am writing a ORACLE select statement with LISTAGG. It works but when I was validating the data, I saw duplicates like 1:1,1:1,2:2,2:2.

I verified that the database do have duplicate. The query is for two tables in a one to many relationship. Below is a snippet of my query but I changed the column names etc..

how can I modified the following query to return unique values for each person?

Thanks

SELECT Table1.PERSON_ID, 
       Table1.FIRST_NAME,
       Table1.MIDDLE_NAME,
       Table1.LAST_NAME,

LISTAGG(case  
        when Table2.DESCRIPTION = '1' then '1:1'
        when Table2.DESCRIPTION = '2' then '2:2'
        when Table2.DESCRIPTION = '3' then '3:3'
        when Table2.DESCRIPTION = '4' then '4:4'
        when Table2.DESCRIPTION = '5' then '5:5'
        when Table2.DESCRIPTION = '6' then '6:6'
        when Table2.DESCRIPTION = '7' then '7:7'
        when Table2.DESCRIPTION = '8' then '8:8'
        when Table2.DESCRIPTION = '9' then '9:9'


      else ''

 end, ',')  
WITHIN GROUP (ORDER BY Table2.DESCRIPTION )  

FROM Table1
LEFT JOIN Table2

ON Table2.PERSON_ID = Table1.PERSON_ID
GROUP BY Table1.PERSON_ID,Table1.FIRST_NAME,Table1.MIDDLE_NAME, Table1.LAST_NAME

Answer 1

Assuming Table2 has PERSON_ID as foreign key pointing to Table1, what you need to do is to replace

FROM Table1
LEFT JOIN Table2
ON Table2.PERSON_ID = Table1.PERSON_ID

with

FROM Table1
LEFT JOIN 
(SELECT DISTINCT PERSON_ID, DESCRIPTION FROM Table2) T2
ON T2.PERSON_ID = Table1.PERSON_ID

and then change Table2 to T2 in LISTAGG() (including in the WITHIN GROUP (ORDER BY ...) clause!)