Excel sum based on lookup of code and values in another table

Question

Given 2 named tables in Excel 2013 (or higher):

tblInvoice

ID    InvRef    Total
1     I/123        45
2     I/234         8

tblDeliveries

ID    InvRef    Amt
1     I/123      10
2     I/123      15
3     I/123      20
4     I/234       5
5     I/234       3

How can we get the tblInvoice[Total] to compute automatically using an Excel formula? i.e. in pseudocode:

 tblDeliveries[Total] = SUM(tblDeliveries[Amt] WHERE MATCH InvRef)

I have tried this Excel formula in tblInvoice[InvTotal] but it is returning an incorrect value:

=SUMPRODUCT(SUMIF(tblDeliveries[InvRef],[InvRef],tblDeliveries[Amt]))

Also tried swapping the first and second parameters. Produces a different amount, but still incorrect:

=SUMPRODUCT(SUMIF([InvRef],tblDeliveries[InvRef],tblDeliveries[Amt]))

If relevant, it is assumed that there is a 1:N relationship from tblInvoice[InvRef]:tblDeliveries[InvRef] and that tblInvoice[InvRef] is UNIQUE.

Answer 1

The syntax is incorrect for what you require.

=SUMPRODUCT(SUMIF(tblDeliveries[InvRef],[@InvRef],tblDeliveries[Amt]))

The @ is the crucial difference.

Regards