SQL sum by year report, looking for an elegant solution - sql

Question

I have a table with 3 columns: ItemCode, Quantity and DocDate.
I would like to create the following report in a more "elegant" way:
SELECT T0.ItemCode,
(SELECT SUM(QUANTITY) FROM MyTable T1 WHERE YEAR(T0.DocDate) = 2011 AND T0.ItemCode = T1.ItemCode) AS '2011',
(SELECT SUM(QUANTITY) FROM MyTable T1 WHERE YEAR(T0.DocDate) = 2012 AND T0.ItemCode = T1.ItemCode) AS '2012'
FROM MyTable T0
GROUP BY T0.ItemCode, YEAR(T0.DocDate)
I'm pretty sure there's a better, more efficient way to write this but I can't come up with the right syntax. Any ideas?

Answer 1

You can try this:
SELECT T0.ItemCode,
SUM(CASE WHEN YEAR(T0.DocDate) = 2011 THEN QUANTITY ELSE 0 END) AS '2011',
SUM(CASE WHEN YEAR(T0.DocDate) = 2012 THEN QUANTITY ELSE 0 END) AS '2012'
FROM MyTable T0
GROUP BY
T0.ItemCode

Answer 2

This type of data transformation is known as a PIVOT. There are several ways that you can perform this operation. You can use the PIVOT function or you can use an aggregate function with a CASE statement:
Static Pivot Version: This is where you hard-code all of the values into the query
select ItemCode, [2011], [2012]
from
(
SELECT ItemCode,
QUANTITY,
YEAR(DocDate) Year
FROM MyTable
) src
pivot
(
sum(quantity)
for year in ([2011], [2012])
) piv
See SQL Fiddle with Demo
Case with Aggregate:
SELECT ItemCode,
SUM(CASE WHEN YEAR(DocDate) = 2011 THEN QUANTITY ELSE 0 END) AS '2011',
SUM(CASE WHEN YEAR(DocDate) = 2012 THEN QUANTITY ELSE 0 END) AS '2012'
FROM MyTable
GROUP BY ItemCode;
See SQL Fiddle with Demo
Dynamic Pivot: The previous two versions will work great is you have a known number of year values to transform, but it you have an unknown number then you can use dynamic sql:
DECLARE #cols AS NVARCHAR(MAX),
#query AS NVARCHAR(MAX)
select #cols = STUFF((SELECT distinct ',' + QUOTENAME(YEAR(DocDate))
from mytable
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)')
,1,1,'')
set #query = 'SELECT itemcode, ' + #cols + ' from
(
select itemcode, quantity, year(docdate) year
from mytable
) x
pivot
(
sum(quantity)
for year in (' + #cols + ')
) p '
execute(#query)
See SQL Fiddle with Demo
All three versions will produce the same result:
| ITEMCODE | 2011 | 2012 |
--------------------------
| 1 | 200 | 45 |
| 2 | 89 | 0 |
| 3 | 0 | 7 |