Find user with higher profits in a postgresql table

Question

I have a table in my database whose structure is like this

sell_id(int) | car_id(int) | worth(int) | date(date) | selled(boolean)

Selled is a wrong 'sold'.

My table is like this

------------------------------
50 |50 |2405 | "2012-07-16" | false
51 |51 |9300 | "2014-10-07" | false
52 |52 |5963 | "2014-11-01" | false
53 |53 |2036 | "2014-09-19" | false
54 |54 |4770 | "2014-01-26" | false
55 |55 |11915| "2010-08-30" | true

Anyway, sell_id is the primary key of this table and a foreign key to a "mother" table. car_id refers to another table as well. Worth is the amount of money a seller sold or bought a car. Date is just when and selled is a boolean to specify whether the seller sold or bought the car. If it is true then he did sell it. Otherwise he bought it.

Now i want to find the user who has made the most value out of selling/buying. This means that he must be the one to have the selled-bought.But i cant figure out the right query.

this query gives me the values of only selling.

select sell_id, sum(worth), selled 
from sellers 
where(selled=true) 
group by sell_id, selled

Some desired result for example would be:

sell_id | total_profits(max)
---------------------------
  51    |     2000

where total_profits would be the maximum worth(where selled=true)-worth(where selled=false)

Any ideas would be really helpfull. Thanks :)

Answer 1

i finally found the answer to my own question. the correct query is :

select sell_id, (sum(worth) - (select sum(worth) 
   from sellers where selled=false group by sell_id 
       order by sum limit 1)) as final from sellers 
             where selled=true   
            group by sell_id order by final desc limit 1