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

Add this trigger to your ExpenseTable

CREATE TRIGGER ExpenseSum AFTER INSERT ON ExpenseTable FOR EACH ROW
BEGIN
    UPDATE ProjectsTable P
    SET ExpenseTotal = 
    (SELECT SUM(ExpenseAmount) from ExpenseTable
    where ExpenseTable.ProjectID= P.ProjectID)
    where P.ProjectID = New.ProjectID;
END

Don't forget to add trigger After Update and After Delete to update ExpenseTotal

Answer 2

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