upidea

with example_table as (
    select 1 as docid, array(3, 5, 8, 2) as rate union all
    select 2 as docid, array(4, 7, 3, 8) as rate union all
    select 3 as docid, array(6, 8, 3, 6) as rate
)
select
    docid,
    rate,
    array_indexof(rate, frate)
from