Divide a column by the Sum of the Column

Question

Hi!
I have a challenge in dividing a column by the total of that same column. What I wan to archive is first check if a column is zero before dividing by the total of the column  and then multiply by 100 to get the percentage of total contribution.
Below is a sample image. I equally will want to round up to 2 decimal places. As it below, the percentage contribution column is derived from the CountOfProduct column
Thanks so much for the help
Zionlite

Answer 1

Use the SUM() OVER() window function, e.g.:
DECLARE @tablename TABLE
product VARCHAR(30) ,
category INT ,
prodcnt INT
INSERT INTO @tablename
VALUES ( 'PROD1', 1, 11 ),
( 'PROD2', 1, 10 ),
( 'PROD3', 2, 13 ),
( 'PROD4', 2, 40 ),
( 'PROD5', 3, 1 );
SELECT O.product ,
O.category ,
O.prodcnt ,
1.0 * O.prodcnt / ( SELECT SUM(I.prodcnt)
FROM @tablename I
FROM @tablename O;
SELECT O.product ,
O.category ,
O.prodcnt ,
1.0 * O.prodcnt / SUM(O.prodcnt) OVER ( )
FROM @tablename O;
SELECT O.product ,
O.category ,
O.prodcnt ,
1.0 * O.prodcnt / ( SELECT SUM(I.prodcnt)
FROM @tablename I
WHERE O.category = I.category
FROM @tablename O;
SELECT O.product ,
O.category ,
O.prodcnt ,
1.0 * O.prodcnt / SUM(O.prodcnt) OVER ( PARTITION BY O.category )
FROM @tablename O;
Data by
Prashanth.
Caveat: For further processing avoid to formatting of the fraction to percent. Do this in the front-end.