sql server compare rows in one table - asp.net

Question

i want to keep track of the changes of a system setup and also to display them in a web application ASP.net VB.
the setup information/data is stored in a table like this:
TABLE 1
| SNR | LENSE | CAMERA | SYS |
|-----|-------|--------|-----|
| 1 | 55mm | rcd30 | 5 | (initial setup sys 5)
| 2 | 80mm | ph1 | 4 | (initial setup sys 4)
| 3 | 80mm | ph1 | 4 | (new setup sys 4)
| 4 | 55mm | ph1 | 5 | (new setup sys 5)
| 5 | 80mm | rcd30 | 5 | (new setup sys 5)
what i want is to compare for both systems (4 and 5) if and which changes occur between setups of the same system and to create a table where i keep the results and from here to display them every time i load the list of setups.
for example if i compare setup's for the sys nr 5, comparing row 1 and 4 there is a difference on camera; between 4 and 5 both the camera and the lense changes. this works if considering the first record for each system as the initial setup.
CHANGES
| SNR | LENSE | CAMERA | SYS |
|-----|-------|--------|-----|
| 1 | n | n | 5 | (initial setup sys 5)
| 2 | n | n | 4 | (initial setup sys 4)
| 3 | n | n | 4 | (new setup sys 4)
| 4 | n | y | 5 | (new setup sys 5)
| 5 | y | y | 5 | (new setup sys 5)
is it possible to do this using SQL? any ideas how? SQL has never been my strongest point :(
edit: using SQL server 2012

Answer 1

If you're using SQL Server 2012 or newer, you can use LAG to find the previous value, and just use a CASE on whether the old and new value differ;
WITH cte AS (
SELECT snr, sys,
lense, LAG(lense) OVER (PARTITION BY sys ORDER BY snr) old_lense,
camera, LAG(camera) OVER (PARTITION BY sys ORDER BY snr) old_camera
FROM table1
)
SELECT snr, sys,
CASE WHEN lense <> old_lense THEN 'y' ELSE 'n' END lense,
CASE WHEN camera <> old_camera THEN 'y' ELSE 'n' END camera
FROM cte
ORDER BY snr;
An SQLfiddle to test with.