is there really no way to do this without using scripting? I have a child custom record linked to a parent custom record. If I create/update a new child custom record instance, I want the related custom field in the parent custom record to be automatically updated (SUM of all the values of the child custom record values).

Probably achievable using custom fields sourced from summary saved search

Actually, that’s what I have at the moment + scheduled workflow every 30 mins. I kinda need this to be real time as this is critical metrics for us.

Right so to have this with a stored field and updated real time you will need a script

If I’m going to script it, is there more efficient way to get the (sum) value? Or is using a summary saved search within the script or by loading a saved search my only option here? Thanks.

I'd probably use a SuiteQL query

SuiteQL supports multiple joins and left outer joins, right?

Correct

Thank you.