Here you go. An updated version of the script that updates the parent record. Update fields as necessary. I removed the line with the getDisplayValue(), but I have a new one to set to get the record. Unfortunately my test instance was wiped this morning and I cannot fully test this code.

var parentTable = 'u_parent_table';

var childTable = 'u_child_table';

var parentField = 'u_parent'; // ref field from child to parent

var numberField = 'u_number'; // what do we want to sum up on the child

var parentTotal = 'u_total';


var sum = new GlideAggregate(childTable);

sum.groupBy(parentField);

sum.addAggregate('SUM', numberField);

sum.query();


var impacts = 0;

while (sum.next()) {

     impacts = sum.getAggregate('SUM', numberField);

     var gr = new GlideRecord(parentTable);

     gr.get(sum.u_parent); // change u_parent to the same as line 3 above

     gr.setValue(parentTotal, impacts);

     gr.update();

}