Use results from one sql query in another where statement (subquery?)

Question

I see many similar questions but they\'re either so complex I can\'t understand them, or they don\'t seem to be asking the same thing.

It\'s simple: I have two colum

Answer 1

SELECT dfid,count(*) 
from downloads_downloads 
WHERE dmid IN (
    SELECT dmid 
    FROM downloads_downloads 
    where dfid = "7024"
)
group by dfid

or using a self join

select t1.dfid,count(*)
from downloads_downloads t1
inner join downloads_downloads t2
on t1.dmid = t2.dmid
where t2.dfid = "7024"

if this takes too long then you will probably need to post an explain plan (google it!)