Left Joins returns duplicate values - mysql

Question

The result I receive:
id sku name GROUP_CONCAT(quantity_received) GROUP_CONCAT(item_cost)
4 00004 Antibacterial Wipes 50,14,25,309,50,14,25,309,50,14,25,309,50,14,25,309,50,14,25,309,50,14,25,309,50,14,25,309,50,14,25,309,50,14,25,309 3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49,3.29,3.29,3.29,3.49
The result I want:
id sku name GROUP_CONCAT(DISTINCT quantity_received) GROUP_CONCAT(DISTINCT item_cost)
4 00004 Antibacterial Wipes 50,14,25,309 3.29,3.49
The way I resolved this issue was placing DISTINCT in the quantity_recieved select. The problem is that if the quantity has two values that are the same such as 50, 50, 14, 25. The result will be 50, 14, 25. I just want to get rid of the repeating numbers and only get the values once.
Here is the query:
SELECT `product`.`id`,`product`.`sku`,`product`.`name`,
case when coalesce(stock1.`quantity`, '') = ''
then '0'
else stock1.`quantity`
end as qty_warehouse,
case when coalesce(sum(distinct stock2.`quantity`), '') = ''
then '0'
else sum(distinct stock2.`quantity`)
end as qty_events,
case when coalesce(stock1.`quantity`, '') = ''
then '0'
else stock1.`quantity`
end +
case when coalesce(sum(distinct stock2.`quantity`), '') = ''
then '0'
else sum(distinct stock2.`quantity`)
end as qty_total
GROUP_CONCAT(DISTINCT quantity_received) ,
GROUP_CONCAT(DISTINCT item_cost)
FROM (`product`)
LEFT JOIN`shipping_event`
ON `shipping_event`.`product_id` = `product`.`id`
LEFT JOIN `product_stock` as stock1
ON `product`.`id` = `stock1`.`product_id` and `stock1`.`location_id` = 112
LEFT JOIN `product_stock` as stock2
ON `product`.`id` = `stock2`.`product_id` and `stock2`.`location_id` != 112
LEFT JOIN `shipping_list`
ON `shipping_event`.`shipping_list_id` = `shipping_list`.`id`
WHERE `shipping_list`.`type` = 'incoming'
AND `shipping_event`.`end_date` > '2004-01-01 01:01:01'
GROUP BY `product`.`id`
ORDER BY `sku` asc LIMIT 20
I am using group concat just to display the result in this case. I actually sum the quantity_received and then multiple them by the item cost.

Answer 1

You could make a subquery with a GROUP BY and then JOIN to the product table.
The same logic can be applied to the other joined tables as well. If you do that, you can skip the GROUP BY product.id:
SELECT p.id
, p.sku
, p.name
, COALESCE(stock1.quantity, 0) --- minor improvements on
AS qty_warehouse --- the long CASE clauses
, COALESCE(SUM(DISTINCT stock2.quantity), 0)
AS qty_events
, COALESCE(stock1.quantity, 0) + COALESCE(SUM(DISTINCT stock2.quantity), 0)
AS qty_total
, grp.all_quantities_received
, grp.all_item_costs
FROM product AS p
LEFT JOIN
( SELECT product_id
, GROUP_CONCAT(se.quantity_received) AS all_quantities_received
, GROUP_CONCAT(se.item_cost) AS all_item_costs
FROM shipping_event AS se
LEFT JOIN shipping_list AS sl
ON se.shipping_list_id = sl.id
WHERE sl.type = 'incoming'
AND se.end_date > '2004-01-01 01:01:01'
GROUP BY se.product_id
) AS grp
ON grp.product_id = p.id
LEFT JOIN `product_stock` AS stock1
ON p.id = stock1.product_id
AND stock1.location_id = 112
LEFT JOIN product_stock AS stock2
ON p.id = stock2.product_id
AND stock2.location_id <> 112
GROUP BY p.id
ORDER BY sku ASC
LIMIT 20