Mysql – Calculation is not correct during in the left join table

MySQLmysql-5.5

At the moment My head is bang on the wall as I have used few of dba.stackexchanged.com example but none of them is working.

AS I'm trying to get SKU that it sold on each Country, as I have 5 country table that it sold.

When I get results and it seems working fine, but the calculation seems wrong

One of the SKU in UK "H-ROOT-M012R-B" in return at QTY_sold_in_uk is '15552' which this calculation are wrong, the correct one is '8' which QTY has sold not '15552'

Here is a code I wrote this https://www.db-fiddle.com/f/u7PxDXy8kzSHV5n8VHC3rY/1
enter image description here

but I keep getting when I use this
https://www.db-fiddle.com/f/qENxYhrqhMHvUMFzYoK4ho/3

enter image description here

When I decided to look around and explore in the StackOverflow and I have used this link pages but results of numbers is keeping return same as the wrong one

multiple sum query with joins

second link multiple sum query with joins

MySQL Count rows from another table for each record in table

I have used inner, left and right join or union seems that calculation is never right.
Here is DB Fiddle I has worked on it
Example code

I know this code is a long one but please bear with me,

    SELECT 
    ti.sku,
    ti.quantity,
    -- UK
    COALESCE((suo_uk.sku), 'Not Sold') AS Unit_in_uk,
    COALESCE(sum(suo_uk.units_ordered), 0) AS QTY_sold_in_uk,

    -- De
    COALESCE((suo_de.sku), 'Not Sold') AS Unit_in_de,
    COALESCE(sum(suo_de.units_ordered), 0) AS QTY_sold_in_de,

    -- Fr
    COALESCE((suo_fr.sku), 'Not Sold') AS Unit_in_fr,
    COALESCE(sum(suo_fr.units_ordered), 0) AS QTY_sold_in_fr,

    -- ES
    COALESCE((suo_es.sku), 'Not Sold') AS Unit_in_es,
    COALESCE(sum(suo_es.units_ordered), 0) AS QTY_sold_in_es,

    -- It
    COALESCE((suo_it.sku), 'Not Sold') AS Unit_in_it,
    COALESCE(sum(suo_it.units_ordered), 0) AS QTY_sold_in_it
FROM
    tbl_inventory AS ti
        LEFT JOIN
    tbl_sku_units_order AS suo_uk ON suo_uk.sku = ti.sku
        LEFT JOIN
    tbl_sku_units_order_de AS suo_de ON suo_de.sku = ti.sku
        LEFT JOIN
    tbl_sku_units_order_fr AS suo_fr ON suo_fr.sku = ti.sku
        LEFT JOIN
    tbl_sku_units_order_es AS suo_es ON suo_es.sku = ti.sku
        LEFT JOIN
    tbl_sku_units_order_it AS suo_it ON suo_it.sku = ti.sku

-- where ti.sku=" H-ROOT-M012R-B"
GROUP BY ti.sku

Please, Advice and your advice would be greatly appreciated.

Best Answer

"Explode-Implode" syndrome causes the inflated SUM.

  1. The JOINs are done. This gives an intermediate table with lots of rows.
  2. SUM() and other aggregates are performed.
  3. The GROUP BY shrinks it back down to a small number of rows.

Where practical, this is a convenient solution; note that there is no JOIN or GROUP BY:

SELECT 
        ( SELECT SUM(...) ... ) AS sum_1,
        ( SELECT SUM(...) ... ) AS sum_2
    FROM ...

But that won't work here. Instead, let's compute the aggregates in "derived" subqueries:

SELECT COALESCE(uk.qty, 0) AS QTY_sold_in_uk,
       COALESCE(de.qty, 0) AS QTY_sold_in_de,
       ...
    FROM  tbl_inventory AS ti
    LEFT JOIN ( SELECT sku, SUM(qty) AS qty ) AS uk  USING(sku)
    LEFT JOIN ( SELECT sku, SUM(qty) AS qty ) AS de  USING(sku)

This way, the aggregation will be confined to the the one table. Also, the LEFT allows for an item not to be sold in some country, then the COALESCE deals with the NULL. Again, no GROUP BY.

This pattern begs for at least 5.6 because the derived tables have no index. However 5.6 will dynamically build one.

Final form

SELECT 
    ti.sku,
    ti.quantity,
    -- UK
    COALESCE(suo_uk.sku, 'Not Sold') AS Unit_sold_in_uk,
    COALESCE(suo_uk.units_ordered, 0) AS QTY_in_uk,
    -- De
    COALESCE(suo_de.sku, 'Not Sold') AS Unit_sold_in_de,
    COALESCE(suo_de.units_ordered, 0) AS QTY_in_de,
    -- Fr
    COALESCE(suo_fr.sku, 'Not Sold') AS Unit_sold_in_fr,
    COALESCE(suo_fr.units_ordered, 0) AS QTY_in_fr,
    -- ES
    COALESCE(suo_es.sku, 'Not Sold') AS Unit_sold_in_es,
    COALESCE(suo_es.units_ordered, 0) AS QTY_in_es,
    -- It
    COALESCE(suo_it.sku, 'Not Sold') AS Unit_sold_in_it,
    COALESCE(suo_it.units_ordered, 0) AS QTY_in_it
FROM
    tbl_inventory AS ti
    LEFT JOIN ( SELECT sku, sum(units_ordered) as units_ordered
                     FROM tbl_sku_units_order
                     GROUP BY sku ) AS suo_uk
                             ON suo_uk.sku = ti.sku
    LEFT JOIN ( SELECT sku, sum(units_ordered) as units_ordered
                     FROM tbl_sku_units_order_de
                     GROUP BY sku ) AS suo_de
                             ON suo_de.sku = ti.sku
    LEFT JOIN ( SELECT sku, sum(units_ordered) as units_ordered
                     FROM tbl_sku_units_order_es
                     GROUP BY sku ) AS suo_es
                             ON suo_es.sku = ti.sku
    LEFT JOIN ( SELECT sku, sum(units_ordered) as units_ordered
                     FROM tbl_sku_units_order_fr
                     GROUP BY sku ) AS suo_fr
                             ON suo_fr.sku = ti.sku
    LEFT JOIN ( SELECT sku, sum(units_ordered) as units_ordered
                     FROM tbl_sku_units_order_it
                     GROUP BY sku ) AS suo_it
                             ON suo_it.sku = ti.sku
    GROUP BY ti.sku
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