SQL How to sum from another table and insert in another table

Question

For now I sum in Delphi app and then insert it in SQL database
but I want database to sum and insert automatically when I insert new ExpenseA

Answer 1

You can create a subquery grouping the expense amount for each project, and then updating the Projects table.

UPDATE ProjectsTable
SET ProjectsTable.ExpenseTotal = S1.ExpenseAmount
FROM ProjectsTable
INNER JOIN (SELECT ProjectID, SUM(ExpenseAmount) as ExpenseAmount
FROM ExpenseTable
GROUP BY ProjectID) as S1
ON ProjectsTable.ProjectID = S1.ProjectID