How to calculate the sum of child elements by field (Nested Sets)?

Question

PHP

Good afternoon.
There is a tree in the database based on the Nested Sets model. I deduce a tree, in other table values ​​communication one-to-many are written down. Values ​​are entered every day at the bottom of the tree. You need to make a query that will get the entire tree from the database and sum up all the values ​​of the descendants on the parent.
Example:
Parent 1: 25pcs (5+15+5) Child
1.1
: 5pcs Child 1.2: 15pcs Child
1:3: 5pcs Parent 2 :
45pcs (20+25 ) 5pcs Descendant 2.1.2: 15pcs Descendant 2.2: 25pcs There can be up to 10 such levels and there will be a large number of tree nodes. Those. you need an optimal solution so that the query is executed as quickly as possible. Thank you.

Answer 1

An example of a tree for clarity