I have a primary table as source of a data entry form. Textboxes of the form are getting their values from the second column of different child tables. All child tables are related to primary table by their primary key's. I need to sum the values in third column of child tables (corresponding to the values in textboxes) and then result goes into the last column of primary table.

I use VBA and database connection to save all the values in primary table from my Form. I want to create a function that calculates the summation and saves it in primary table with OnClick event of the existing save button.

Please let me know what is the best approach?

Please let me know if given information is not enough or I am not clearly explain it.

Thanks