I have a table that looks like this:
Date Time A/B Row*
1/1 8:00 A 1
1/1 8:10 A 1
1/1 8:20 B 2
2/1 8:00 B 2
2/1 8:10 A 3
3/1 8:00 B 4
3/1 8:10 A 5
3/1 8:20 A 5

I need to create a new coloumn like ROW_NUMBER() but row number will only change if A/B(i)<>A/B(i+1) - wanted output in red
Thanks in advance!