MYSQL Join to get data in specific format - php

Question

I've recently changed updated my database with a couple of new tables and having trouble to get(select) data from three different tables.
There are 4 stores which exchange stock with each other, it gets recorded in database.
Table 'sites' has store id and name info.
CREATE TABLE `sites` (
`id` int(10) NOT NULL,
`name` varchar(35) NOT NULL
)
Table 'stock_exchange_new' has info about stock transfer date, from
store, to store etc.
CREATE TABLE `stock_exchange_new` (
`id` int(11) NOT NULL,
`transfer_date` date NOT NULL,
`from_site` int(11) NOT NULL,
`to_site` int(11) NOT NULL,
`transfer_ref` varchar(255) NOT NULL,
`note` varchar(300) NOT NULL,
`added_by` int(11) NOT NULL,
`added_at` datetime NOT NULL,
`edited_by` int(11) NOT NULL,
`edited_at` datetime NOT NULL
)
Table 'stock_item_txns' has the information about what item was
exchanged/transferred:
CREATE TABLE `stock_item_txns` (
`id` int(11) NOT NULL,
`stock_exchange_id` int(11) NOT NULL,
`item_id` int(11) NOT NULL,
`units_per_ctn` int(11) NOT NULL,
`qty` decimal(10,2) NOT NULL,
`ctn_price` decimal(10,2) NOT NULL,
`total_price` decimal(10,2) NOT NULL
)
Now, for one particular store, I need the data shown as compare to itself, eg: for Store 1, it should be something like this:
Store Name Total_Sent Total_Received
Store2 500 200
Store3 490 580
Store4 300 400
Tried so far...
SELECT GREATEST(s1.name, s2.name) AS from_store,
LEAST(s1.name, s2.name) AS to_store,
SUM(CASE WHEN s1.name < s2.name THEN si.total_price ELSE 0 END) AS received,
SUM(CASE WHEN s1.name > s2.name THEN si.total_price ELSE 0 END) AS sent
FROM stock_exchange_new se
INNER JOIN sites s1
ON se.from_site = s1.id
INNER JOIN sites s2
ON se.to_site = s2.id
INNER JOIN stock_item_txns si
ON se.id = si.stock_exchange_id
GROUP BY GREATEST(se.from_site, se.to_site),
LEAST(se.from_site, se.to_site)
HAVING MAX(GREATEST(se.from_site, se.to_site)) = '1'
Here's the fiddle, for better understanding.

Answer 1

Utilising a couple of sub queries, something like this (not tested):-
SELECT s2.name AS 'Store Name',
from_site_total,
to_site_total
FROM sites s1
CROSS JOIN sites s2
LEFT OUTER JOIN
(
SELECT from_site,
to_site,
SUM(stock_item_txns.total_price) AS from_site_total
FROM stock_exchange_new
INNER JOIN stock_item_txns ON stock_exchange_new.id = stock_item_txns.stock_exchange_id
GROUP BY from_site,
to_site
) sub_from_site
ON s1.id = sub_from_site.from_site
AND s2.id = sub_from_site.to_site
LEFT OUTER JOIN
(
SELECT to_site,
from_site,
SUM(stock_item_txns.total_price) AS to_site_total
FROM stock_exchange_new
INNER JOIN stock_item_txns ON stock_exchange_new.id = stock_item_txns.stock_exchange_id
GROUP BY to_site,
from_site
) sub_to_site
ON s1.id = sub_to_site.to_site
AND s2.id = sub_to_site.from_site
WHERE s1.name = 'Store1'
AND s2.name != 'Store1'