Just a couple of typo points really.

The function SumCustomerTotals returns a table with CustomerTotalDue and shippedtotal but your example function call in the 6th code box selects different column names. (I think the function name was wrong originally but is fixed now).

I also wondered if the last code box should be split to have just the GetMinOrderDates function declaration in one box and the GetSalesReport_Optimize1 procedure in a seperate box.

Avidly reading these two articles as I'm still trying to 'unlearn' the procedural mindset! Thanks.