SQL select and order by (count of related records inside a second table) subtracted by (count of related records inside second table with condition) - sql

Question

I am trying to SELECT every record in a table one ORDERed BY the COUNT of records inside a second table that store the related primary key value and WHERE 'positive' is true, subtracted by the COUNT of records inside the second table that store the related primary key value and WHERE 'positive' is false.
Here is my database structure
Table 1
id
data
0
zero
1
one
2
two
3
three
Table 2
id
related_tableone_id
positive
0
1
0
1
2
1
2
2
0
3
2
1
4
3
1
5
3
1
Here is what I am trying to get
id
data
subtracted_counts (i dont need this but these values are what the records should be ordered by)
3
three
2
2
two
1
0
zero
0
1
one
-1
For better understanding on what i want to achieve:
This database structure can be compared with a voting system, where
Table 1 are entities that can be voted up or voted down.
In this case, Table 2 would store the votes with positive=true for an upvote and positive=false for a downvote.
The goal is to get all entities ORDERed BY their summarized vote value.
(Within a single query)
My research
I found this post
SQL - How To Order Using Count From Another Table, tho there is no subtraction logic
I tried this query
SELECT
tableone.*,
COUNT(related_tableone_id) - COUNT(negative_related_tableone_id) AS subtracted_count
FROM
tableone
LEFT JOIN
(SELECT related_tableone_id
FROM tabletwo
WHERE positive = true) AS positives ON tableone.id = positives.related_tableone_id
LEFT JOIN
(SELECT related_tableone_id AS negative_related_tableone_id
FROM tabletwo
WHERE positive = false) AS negatives ON tableone.id = negatives.negative_related_tableone_id
GROUP BY
tableone.id
ORDER BY
subtracted_count DESC;
But it doesn't subtract the counts right for some reason and there is probably a more clear solution

Answer 1

Use a LEFT join of Table1 to Table2 and conditional aggregation in the ORDER BY clause:
SELECT t1.id, t1.data
FROM Table1 t1 LEFT JOIN Table2 t2
ON t2.related_tableone_id = t1.id
GROUP BY t1.id
ORDER BY SUM(CASE t2.positive WHEN true THEN 1 WHEN false THEN -1 ELSE 0 END) DESC;
or, a correlated subquery in the ORDER BY clause (which may perform better):
SELECT t1.*
FROM Table1 t1
ORDER BY (
SELECT COALESCE(SUM(CASE t2.positive WHEN true THEN 1 WHEN false THEN -1 END) , 0)
FROM Table2 t2
WHERE t2.related_tableone_id = t1.id
) DESC;
See the demo (works in MySql, Postgresql and SQLite).

Answer 2

A single subquery can count both upvotes and downvotes, using conditional aggregation. I would use a lateral join to do the computation:
select t1.*, t2.*
from tableone t1
cross join lateral (
select
sum(case when t2.positive = true then 1 else 0 end) upvotes,
sum(case when t2.positive = false then 1 else 0 end) downvotes
from tabletwo t2
where t2.related_tableone_id = t1.id
) t2
order by t2.upvotes - t2.downvotes desc, t1.id
Depending on your database, the lateral join might be introduced by cross applyinstead (eg in Oracle or SQL Server).