How to calculate the sum of values in a tree using SQL

Question

I need to sum points on each level earned by a tree of users. Level 1 is the sum of users\' points of the users 1 level below the user. Level 2 is the Level 1 points of the

Answer 1

SQL in general, like others said, does not handle well such relations. Typically, a surrogate 'relations' table is needed (id, parent_id, unique key on (id, parent_id)), where:

• every time you add a record in 'table', you:

  INSERT INTO relations (id, parent_id) VALUES ([current_id], [current_id]);

  INSERT INTO relations (id, parent_id) VALUES ([current_id], [current_parent_id]);

  INSERT INTO relations (id, parent_id) SELECT [current_id], parent_id FROM relations WHERE id = [current_parent_id];

• have logic to avoid cycles

• make sure that updates, deletions on 'relations' are handled with stored procedures

Given that table, you want:

SELECT rel.parent_id, SUM(tbl.points)
FROM table tbl INNER JOIN relations rel ON tbl.id=rel.id
WHERE rel.parent_id <> 0
GROUP BY rel.parent_id;

Answer 2

I would say: create a stored procedure, probably has the best performance. Or if you have a maximum number of levels, you could create subqueries, but they will have a very poort performance.

(Or you could get MS SQL Server 2008 and get the new hierarchy functions... ;) )

Answer 3

You have a couple of options:

1. Use a cursor and a recursive user-defined function call (it's quite slow)
2. Create a cache table, update it on INSERT using a trigger (it's the fastest solution but could be problematic if you have lots of updates to the main table)
3. Do a client-side recursive calculation (preferable if you don't have too many records)