I have a table foo( userid integer, data integer); with the constraint unique(userid,data)
Now I wish to select one userid and calculate the differences between the data -values (when they are sorted) . For example if the table contains:
4, 100 5, 200 5, 210 5, 231
I want the values
5,10 5,21
what should happen to the 4,100 record you may ask, I will try to exclude that case by requireing each userid to have at least two data values.
The question is now: is there a clever and efficient way of calculating these differences in data values?
The only thing I can think of is picking a data value and select min(data) from foo where userid=5 and data>200 and then calculate the difference and do what I want with it, and the repeat this process with the last selected data value. I guess that will work, but I'm curious, are there other ways?
