Rod Edwards shows off a great use case for LAG():
I often find myself using windows functions in order to group data in wierd and wonderful ways that a simple GROUP BY can’t do… however, the example below is one I came across quite recently on my travels, I was asked to have a look at some code for optimization opportunities. And in this case, thankfully there were some.
Read on for a lengthy cursor, followed by a much less lengthy (and much faster) window function.