Subtracting one row of data from another in SQL

Question

I\'ve been stumped with some SQL where I\'ve got several rows of data, and I want to subtract a row from the previous row and have it repeat all the way down.

So her

Answer 1

Select f1.id, f1.seqnum, f2.seqnum, f1.length, f2.length, f1.length-f2.length 

From (

Select Id, length, row_number(order by length) 'seqnum'
From
foo

) f1

Inner join (

Select 
Id, length, row_number(order by length) 'seqnum' from foo union select 0, 0, 0

) f2 

On f1.seqnum = f2.seqnum + 1

Order by f1.length desc