How to group by with a special condition

Question

Currently when I issue this SQL, it gets the distinct username.

I have some distinct usernames, which represent groups, e.g. GRP_BSN.

I would li

Answer 1

Not very efficient, but should work:

SELECT 
    CASE WHEN username LIKE 'GRP%' THEN username ELSE 'GRP_OTHERS' END AS username, 
    COUNT(*)
FROM host
WHERE seq BETWEEN 0 AND 2000
GROUP BY CASE WHEN username LIKE 'GRP%' THEN username ELSE 'GRP_OTHERS' END;

Answer 2

If you wanted to do it by putting small groups into one bucket, instead of by a particular name pattern, you could use:

select (case when cnt > 100 then username else 'OTHER' end), sum(cnt) as cnt
from (select username, count(*) as cnt
      from host
      where seq between 0 and 2000
      group by username
     ) t
group by (case when cnt > 100 then username else 'OTHER' end)

Answer 3

@bfavaretto is nice (+1 to him), but if you don't know about username prefix or they are different you can go with something like:

GROUP BY CASE
             WHEN REGEXP_LIKE(username, '^\d+$') THEN 'GRP_OTHERS'
                                                 ELSE username
         END