Not sure if there is any way to do this, but it seems like there should be.
I have a table which needs to do calculations using data from multiple child records (summed up) in order to function properly.
__UNIT PRICE MATERIAL A
__QTY MATERIAL A ---- (7, from below)
__TOTAL PRICE MATERIAL A
__PIECE | QUANTITY MATERIAL A
____PC A | 2
____PC B | 4
____PC C |1
How can I go about achieving this?