WITH base AS(
    SELECT user_id,
           fdate - ROW_NUMBER() OVER (PARTITION BY user_id ORDER BY fdate) AS grp_key
    FROM tb_dau 
),

t AS (
    SELECT user_id, count(grp_key)AS cnt
    FROM base
    GROUP BY user_id, grp_key
) 

SELECT user_id, MAX(cnt) AS max_consec_days
FROM t
GROUP BY user_id;