Row combination choices based on condition - MySQL - mysql

Question

I have a working SQL query which returns the following results:
What I'm looking to be able to do is for MySQL to calculate the sum of the weight column and present combinations of rows from the above table in which the sum(Weight) <= 300. An example of the expected results using the table above would be:
My questions about this are: is this possible from with MySQL? Would I need to execute multiple SQL queries and how would I be able to produce the results illustrated above? Is it possible to achieve the first table and the combinations from one query?

Answer 1

Disclaimer: I'm not sure how exactly you envision returning 3 result sets from one query, and why there are only three -- (1,4) and (2,3) would also be valid combinations. So, I'll assume it was just a general example, and you want the complete result in some form.
Let's say you have this table (I've added one row to make it more generic, you example would only produce 2-element combinations):
MariaDB [test]> SELECT * FROM t1;
+------+--------+
| id | weight |
+------+--------+
| 1 | 100 |
| 2 | 120 |
| 3 | 200 |
| 4 | 96 |
| 5 | 50 |
+------+--------+
5 rows in set (0.00 sec)
With MariaDB 10.2, you can use a recursive CTE to achieve your goal, e.g.
WITH RECURSIVE comb(id,ids,weights,sumweight) AS (
SELECT
id,
CAST(t1.id AS CHAR) AS ids,
CAST(weight AS CHAR) AS weights,
weight AS sumweight
FROM t1
WHERE weight <= 300
UNION
SELECT
t1.id AS id,
CONCAT(comb.ids,',',t1.id) AS ids,
CONCAT(comb.weights,',',weight) AS weights,
t1.weight + comb.sumweight AS sumweight
FROM t1 JOIN comb ON (comb.id < t1.id)
HAVING sumweight <= 300
) SELECT ids, weights, sumweight FROM comb;
You'll get this:
+-------+------------+-----------+
| ids | weights | sumweight |
+-------+------------+-----------+
| 1 | 100 | 100 |
| 2 | 120 | 120 |
| 3 | 200 | 200 |
| 4 | 96 | 96 |
| 5 | 50 | 50 |
| 1,2 | 100,120 | 220 |
| 1,3 | 100,200 | 300 |
| 1,4 | 100,96 | 196 |
| 1,5 | 100,50 | 150 |
| 2,4 | 120,96 | 216 |
| 2,5 | 120,50 | 170 |
| 3,4 | 200,96 | 296 |
| 3,5 | 200,50 | 250 |
| 4,5 | 96,50 | 146 |
| 1,2,5 | 100,120,50 | 270 |
| 1,4,5 | 100,96,50 | 246 |
| 2,4,5 | 120,96,50 | 266 |
+-------+------------+-----------+
17 rows in set (0.00 sec)
The query above is not perfect, it is just to give an idea of the possible solution. The result seems correct, and you can improve and polish representation according to your needs.
For your second question, "Is it possible to achieve the first table and the combinations from one query?", you didn't say how you got the first table, so it's hard to give a precise example, but in any case it surely should be possible. The most obvious way is to take whatever query you used to get that result set, wrap it into a view, and then use this view instead of t1 table in the above example.