Calculate % using OVER() for each row in SQL Server 2012 -

i needed guidance question on how calculate percentage between 2 cells on each row. on sql server 2012. below structure of current dataset.

customer_number    price_last_year      price_today --------------------------------------------------- 909523                   154               190 20175808                 154               100 21808187                 154               190 22792798                 184               284 23256155                 154               230 

basically, trying include additional column calculates percentage of (price_today)/price_last_year) each specific row. using windowing over() function , has not worked properly.

this how want new dataset like:

customer_number price_last_year     price_today     percentage_as oftoday% 909523                   154               190                 23.3% 20175808                 154                  100             -35.1% 21808187                 154               190                 23.3% 22792798                 184               284                 54.3% 23256155                 154               230                 49.3%  

this query percentage calculation:

select distinct    customer_number,    price_last_year,    price_today,    [percentage of today%]=sum(price_today)100.0/(price_last_year) over()     tabl2 group     customer_number, price_today, price_last_year 

i have tried number of variations percentage over() calculation. tried [percentage of today%]=sum(price_today)100.0/(price_last_year) over() (partition customer_number), , throws error.

how can calculate percentage using over() each row?

if calculation between 2 columns of same row don't need over() clause or group by clause - divide two. subtracting 1 , multiplying 100 should give nice percentage representation:

select customer_number,         price_last_year,         price_today,         (1 - (price_today/price_last_year)) * 100 [percentage of today%]   tabl2