MySQL query -- retrieve data from two different years - mysql

Question

I cannot seem to get this MySQL query right. My table contains yearly inventory data for retail stores. Here's the table schema:
CREATE TABLE IF NOT EXISTS `inventory_data` (
inventory_id int unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,
store_id smallint unsigned NOT NULL,
inventory_year smallint unsigned NOT NULL,
shortage_dollars decimal(10,2) unsigned NOT NULL
)
engine=INNODB;
Every store is assigned to a district which in this table (some non-relevant fields removed):
CREATE TABLE IF NOT EXISTS `stores` (
store_id smallint unsigned NOT NULL AUTO_INCREMENT PRIMARY KEY,
district_id smallint unsigned not null
)
engine=INNODB;
I want to be able to retrieve the shortage dollar amounts for two given years for all the stores within a given district. Inventory data for each store is only added to the inventory_data table when the inventory is completed, so not all stores within a district will all be represented all the time.
This query works to return inventory data for all stores within a given district for a given year (ex: stores in district 1 for 2012):
SELECT stores.store_id, inventory_data.shortage_dollars
FROM stores
LEFT JOIN inventory_data ON (stores.store_id = inventory_data.store_id)
AND inventory_data.inventory_year = 2012
WHERE stores.district_id = 1
But, I need to be able to get data for stores within a district for two years, such that the data looks something close to this:
store_id | yr2011 | yr2012

Answer 1

For the specific result format that you need, you may try the following query:
SELECT `s`.`store_id`, `i`.`shortage_dollars` AS `yr2011`, `i1`.`shortage_dollars` AS `yr2012`
FROM `stores` `s`
LEFT JOIN `inventory_data` `i` ON `s`.`store_id` = `i`.`store_id`
AND `i`.`inventory_year` = 2011
LEFT JOIN `inventory_data` `i1` ON `s`.`store_id` = `i1`.`store_id`
AND `i1`.`inventory_year` = 2012
WHERE `s`.`district_id` = 1
Alternatively, you may as well try the next simpler query.
SELECT `s`.`store_id`, `i`.`inventory_year`, `i`.`shortage_dollars`
FROM `stores` `s`
LEFT JOIN `inventory_data` `i` ON `s`.`store_id` = `i`.`store_id`
WHERE `s`.`district_id` = 1
AND `i`.`inventory_year` IN (2011, 2012)
ORDER BY `s`.`store_id`, `i`.`inventory_year`
Hope it helps!

Answer 2

SELECT
stores.store_id,
inventory_data.inventory_year
inventory_data.shortage_dollars
FROM
(SELECT * FROM stores district_id = 1) stores
LEFT JOIN
(SELECT * FROM inventory_data
WHERE inventory_year IN (2011,2012)) inventory_data
USING (store_id)
;
or
SELECT
stores.store_id,
GROUP_CONCAT(inventory_data.shortage_dollars) dollars_per_year
FROM
(SELECT * FROM stores district_id = 1) stores
LEFT JOIN
(SELECT * FROM inventory_data
WHERE inventory_year IN (2011,2012)) inventory_data
USING (store_id)
GROUP BY stores.id,inventory_year;