SQL subqueries using SELECTs only - sql

Question

I need to write a query with subqueries using SELECT and aggregation functions only, e.g.:
select distinct m_name
from MANUFACT
where m_id in (select TOP 1 m_id
from PRODUCT
where p_id = (select p_id
from PRODUCT
where p_desc = 'Bronze Sculpture'));
The question is about query similar to this one, but using SUM(). The data I have:
Table SPERSON:
sp_id | sp_name
---------------
10 | Jones
39 | Matsu
23 | Atsuma
Table SALE:
sp_id | qty
-----------
10 | 20
23 | 30
10 | 10
39 | 20
etc.
The task is to return the sp_name s whose total number of products is <= 75.
The teacher says we're not allowed to use join, but I doubt whether is any way not to use it.
This is what I have so far:
select sp_name
from SPERSON
where sp_id in (select sp_id from SALE
where qty in (select sum(qty) group by sp_id));
Anyway, I only got the 'Each GROUP BY expression must contain at least one column that is not an outer reference' error, but can't really get the thing.

Answer 1

You can use correlated subquery :
SELECT q.sp_name
FROM( SELECT sp_name,
(SELECT SUM(qty) FROM sale s WHERE s.sp_id = p.sp_id ) AS qty
FROM SPERSON p
GROUP BY sp_name
) q
GROUP BY q.sp_name
HAVING SUM(q.qty) <= 75
Mostly, using correlated subqueries, which may contains a reference to the outer query and so produces different results for each row of the outer query, is not suggested. But I suggested to use it as an alternative method depending on your case for not being permitted to use JOIN. Btw, it is more straightforward to use JOIN .

Answer 2

You can try to approach a problem from different direction.
Create a query to calculate total quantity grouped by sp_id
SELECT s.sp_id, SUM(s.qty)
FROM SALE s
GROUP BY s.sp_id
Filter persons id which has quantity less or equal to 75
SELECT s.sp_id, SUM(s.qty)
FROM SALE s
GROUP BY s.sp_id
HAVING SUM(s.qty) <= 75
Because joins not allowed, "inject" name as a subquery
SELECT
(SELECT p.sp_name FROM SPERSON p WHERE p.sp_id = s.sp_id) AS name
FROM SALE s
GROUP BY s.sp_id
HAVING SUM(s.qty) <= 75