Difference between rows

[sheederj]

Hi,
I am trying to compute a variable "weight gained since last visit". So, I have the weight at each visit and I'd like the query to compute the difference since the last visit. The fields in the table are:

Patient
Visit date
Weight

Thanks very much for any help!
-j

 

[pbaldy]

One way:

http://www.baldyweb.com/PrevValue.htm

 

[sheederj]

That was perfect! Thanks so much for you help!