sql query to set year as column name - mysql

Question

By writing the following query
SELECT item_name, YEAR( DATE ) , SUM( item_sold_qty )
FROM item
JOIN sales ON item.id = sales.item_number
GROUP BY YEAR( DATE ) , item_name
ORDER BY item_name
i'm able to get the following result
item_name YEAR( DATE ) SUM( item_sold_qty )
pencil 2011 22
pencil 2012 44
eraser 2012 22
eraser 2011 11
pen 2012 66
pen 2011 33
nib 2012 88
nib 2011 44
Instead i want the result in the following way
item_name 2011 2012
pencil 22 44
eraser 11 22
pen 33 66
nib 44 88
I'm not really good at sql and have no clue for how to set the years as column names.
Need help.
NOTE :: My database has 2 tables. Sales table has date column which has different dates like 2012-03-01, 2012-04-02, 2011-07-03, so on...

Answer 1

Maybe something like this:
SELECT
item_name,
SUM(CASE WHEN YEAR( DATE )=2011 THEN item_sold_qty ELSE 0 END) AS '2011',
SUM(CASE WHEN YEAR( DATE )=2012 THEN item_sold_qty ELSE 0 END) AS '2012'
FROM
item
JOIN sales ON item.id = sales.item_number
GROUP BY
item_name
ORDER BY
item_name
EDIT
If you want the other years and still sum them. Then you can do this:
SELECT
item_name,
SUM(CASE WHEN YEAR( DATE )=2011 THEN item_sold_qty ELSE 0 END) AS '2011',
SUM(CASE WHEN YEAR( DATE )=2012 THEN item_sold_qty ELSE 0 END) AS '2012',
SUM(CASE WHEN NOT YEAR( DATE ) IN (2011,2012) THEN item_sold_qty ELSE 0 END) AS 'AllOtherYears'
FROM
item
JOIN sales ON item.id = sales.item_number
GROUP BY
item_name
ORDER BY
item_name
EDIT2
If you have a lot of years and you do not want to keep on adding years. Then you need to using dynamic sql. That means that you concat a varchar of the sql and then execute it.
Useful References:
MySQL pivot table with dynamic headers based on single column data
How To have Dynamic SQL in MySQL Stored Procedure
MySQL/Pivot table
MYSQL - Rows to Columns

Answer 2

The answer above will work but adding a case for ever year may or may not be suitable.
If you're on a PHP platform you could change the layout of your existing array like such
foreach($items as $item)
{
$item_names[$item[item_name]][$item[year]] += $item[item_sold_qty];
}
This will make an array as follows:
Array
(
[pencil] => Array
(
[2011] => 22
[2012] => 44
)
[eraser] => Array
(
[2012] => 22
[2011] => 11
)
[pen] => Array
(
[2012] => 66
[2011] => 33
)
[nib] => Array
(
[2012] => 88
[2011] => 44
)
)
Also change your original query to assign better names to the variables:
SELECT item_name, YEAR( DATE ) as year , SUM( item_sold_qty ) as item_sold_qty
FROM item
JOIN sales ON item.id = sales.item_number
GROUP BY YEAR( DATE ) , item_name
ORDER BY item_name
The above assumes your mysql result array looks something like this:
Array
(
[0] => Array
(
[item_name] => pencil
[year] => 2011
[item_sold_qty] => 22
)
[1] => Array
(
[item_name] => pencil
[year] => 2012
[item_sold_qty] => 44
)
[2] => Array
(
[item_name] => eraser
[year] => 2012
[item_sold_qty] => 22
)
[3] => Array
(
[item_name] => eraser
[year] => 2011
[item_sold_qty] => 11
)
[4] => Array
(
[item_name] => pen
[year] => 2012
[item_sold_qty] => 66
)
[5] => Array
(
[item_name] => pen
[year] => 2011
[item_sold_qty] => 33
)
[6] => Array
(
[item_name] => nib
[year] => 2012
[item_sold_qty] => 88
)
[7] => Array
(
[item_name] => nib
[year] => 2011
[item_sold_qty] => 44
)
)

Answer 3

Here:
SELECT
i.item_name,
SUM(s1.item_sold_qty) AS '2011',
SUM(s2.item_sold_qty) AS '2012'
FROM item i
LEFT JOIN sales s1 ON (i.id = s1.item_number AND YEAR(s1.DATE) = 2011)
LEFT JOIN sales s2 ON (i.id = s2.item_number AND YEAR(s2.DATE) = 2012)
GROUP BY i.item_name
ORDER BY i.item_name
Of course, you will have to add as many joins as many years you want to search through...