Need help in using REGEXP function

SELECT ID,
     CASE WHEN listagg(
            DISTINCT col_1,',') WITHIN GROUP(ORDER BY col_1)= '' THEN 'null' 
            ELSE (lower(LISTAGG(distinct col_1,',') WITHIN GROUP ( ORDER BY col_1))) END AS Col_001
        FROM 
            (SELECT distinct B.ID, date, timestamp, 
            TRY_CAST(pno as INTEGER) as pno,
            REGEXP_REPLACE(col_1,'\http.*$|null', '') as col_1
            FROM 
            table1 B LEFT JOIN table2 D ON D.ID=B.ID
            WHERE B.ID IN('5871162','35915895')
            and date='2021-11-02'
            ORDER BY pno) 
            GROUP BY ID;

When I run the above query, I’m getting results like

ID                 COL_001

5871162            ,monthend_offer
35915895           dec_cashback,dec_offer

If I replace comma with empty string, the result will be like mentioned below and that is not the excepted result

    5871162            monthend_offer
    35915895           dec_cashbackdec_offer

I want to replace only the comma ‘,’ from the first record. The record should display like below:

5871162            monthend_offer
35915895           dec_cashback,dec_offer

I want to replace only the LEADING comma

Any guidance on how to implement this?

>Solution :

SELECT 
    column1, 
    ltrim(column1, ','),
    regexp_replace(column1, '^,')
FROM VALUES
    (',monthend_offer'),
    ('dec_cashback,dec_offer');