sum function in table Validated Value set

Summary

sum function in table Validated Value set

Content

Requirement is to fetch the total donations made by an employee in a particular year to use in the donation Rule fast formula.I didn't find any DBI to fetch the donations.So thought of creating a value set(Validation Type is Table) to fetch the total hours donated by an employee.and planning to use the same in fast formula.

But when i am trying to fetch the sum of a column it is throwing an error.please refer the attachment for details of the value set.

Please suggest how i can achieve this.