Reuse query statements in SQL with Cross Apply

Have you ever had a situation where you needed to repeat code in an SQL command?

I had many times, and I used to copy and paste the code snipped.

As a consequence, every time a change or a fix needs to be made, it is necessary to be careful and remember to change all the places where it was replicated.

Here is an example: the subtotal is a calculated field, and it is also being used in the where clause

Select I.Quantity * I.Price as SubTotal
from InvoiceItem I
where I.Quantity * I.Price > 100        

Here is the same query, with the calculation centered in a cross-apply:

Select Calc.SubTotal
from InvoiceItem I
cross apply (
	select I.Quantity * I.Price as SubTotal
) Calc
where Calc.SubTotal > 100