Remove duplicate values from comma separated variable in Oracle - sql

Question

I have a variable (called: all_email_list) which contains 3 email address lists altogether. (I found some similar question but not the same with a proper solution)
Example: test#asd.com, test2#asd.com,test#asd.com,test3#asd.com, test4#asd.com,test2#asd.com (it can contain spaces between comas but not all the time)
The desired output: test#asd.com, test2#asd.com,test3#asd.com,test4#asd.com
declare
first_email_list varchar2(4000);
second_email_list varchar2(4000);
third_email_list varchar2(4000);
all_email_list varchar2(4000);
begin
select listagg(EMAIL,',') into first_email_list from UM_USER a left join UM_USERROLLE b on (a.mynetuser=b.NT_NAME) left join UM_RULES c on (c.id=b.RULEID) where RULEID = 902;
select listagg(EMAIL,',') into second_email_list from table2 where CFT_ID =:P25_CFT_TEAM;
select EMAIL into third_email_list from table3 WHERE :P25_ID = ID;
all_email_list:= first_email_list || ',' || second_email_list || ',' || third_email_list;
dbms_output.put_line(all_email_list);
end;
Any solution to solve this in a simple way? By regex maybe.

Answer 1

Solution description. Use CTE to first split up the list of emails into rows with 1 email address per row (testd_rows). Then select distinct rows (testd_rows_unique) from testd_rows and finally put them back together with listagg. From 19c onwards you can use LISTAGG with the DISTINCT keyword.
set serveroutput on size 999999
clear screen
declare
all_email_list varchar2(4000);
l_unique_email_list varchar2(4000);
begin
all_email_list := 'test#asd.com, test2#asd.com,test#asd.com,test3#asd.com, test4#asd.com,test2#asd.com';
WITH testd_rows(email) AS
(
select regexp_substr (all_email_list, '[^, ]+', 1, rownum) split
from dual
connect by level <= length (regexp_replace (all_email_list, '[^, ]+')) + 1
), testd_rows_unique(email) AS
(
SELECT distinct email FROM testd_rows
)
SELECT listagg(email, ',') WITHIN GROUP (ORDER BY email)
INTO l_unique_email_list
FROM testd_rows_unique;
dbms_output.put_line(l_unique_email_list);
end;
/
test2#asd.com,test3#asd.com,test4#asd.com,test#asd.com
But ... why are you converting rows to a comma separated string and then de-duping it ? Use UNION to take out the duplicate values in a single SELECT statement and do LISTAGG on the values. No regexp needed then. UNION will skip duplicates as opposed to UNION ALL which returns all the rows.
DECLARE
all_email_list varchar2(4000);
BEGIN
WITH all_email (email) AS
(
select email from UM_USER a left join UM_USERROLLE b on (a.mynetuser=b.NT_NAME) left join UM_RULES c on (c.id=b.RULEID) where RULEID = 902
UNION
select email from table2 where CFT_ID =:P25_CFT_TEAM
UNION
select email from table3 WHERE :P25_ID = ID
)
SELECT listagg(email, ',') WITHIN GROUP (ORDER BY email)
INTO all_email_list
FROM all_email;
dbms_output.put_line(all_email_list);
END;
/

Answer 2

You could leverage the apex_string.split table function to simplify the code.
12c+ makes it real clean
select listagg(distinct column_value,',') within group (order by null)
from apex_String.split(replace('test#asd.com, test2#asd.com,test#asd.com,test3#asd.com, test4#asd.com,test2#asd.com'
,' ')
,',')
11g needs a wrapping table() and listagg doesn't support distinct.
select listagg(email,',') within group (order by null)
from
(select distinct column_value email
from table(apex_String.split(replace('test#asd.com, test2#asd.com,test#asd.com,test3#asd.com, test4#asd.com,test2#asd.com',' '),','))
);