Question

I have three tables: objects, relations, points

Relations table connects multiple points to objects. Imagine table structure like this:

**OBJECTS**
  |object_id|object_name|object_points|
**RELATIONS**
  |relation_id|relation_object_id|relation_point_id|
**POINTS**
  |point_id|point_value(INT)|

No how can i make “double join” in UPDATE to renew object table field object_points from total sum of related point_values?

Answer 1

Something like this?

UPDATE
        Objects AS o
    JOIN
        ( SELECT 
              r.relation_object_id
            , SUM(point_value) AS total_points
          FROM
                  Relations AS r
              JOIN
                  Points AS p
                ON p.point_id = relation_point_id 
          GROUP BY
              r.relation_object_id
        ) AS grp
      ON grp.relation_object_id = o.object_id
SET
    o.object_points = grp.total_points ;