Setting user defined variables with joins - mysql

Question

I have a query like below:
Result gives #sold_count:=SUM(I.quantity) = 10, but #sold_count = 0,
so calculations are all 0.
What should be wrong here?
SET #sold_count :=0;
SELECT
#sold_count:=SUM(I.quantity),
#sold_count,I.from_widget,COUNT(from_widget) as order_count,
(#sold_count * buy_price) as ciro,
(#sold_count * list_price) as liste_ciro,
(#sold_count * widget_price) as vitrin_ciro,
P.*
FROM
tbl_products P
LEFT JOIN tbl_order_items I on I.product_id = P.id
WHERE
P.publish_date BETWEEN DATE_SUB( CURDATE( ) ,INTERVAL 3 MONTH ) AND DATE_SUB( CURDATE( ) ,INTERVAL 0 MONTH )
GROUP BY I.from_widget,I.product_id
ORDER BY publish_date DESC

Answer 1

Don't use variables. Just:
SELECT
SUM(I.quantity),
I.from_widget,
COUNT(from_widget) AS order_count,
SUM(I.quantity) * buy_price AS ciro,
SUM(I.quantity) * list_price AS liste_ciro,
SUM(I.quantity) * widget_price AS vitrin_ciro,
P.*
FROM
tbl_products P
LEFT JOIN tbl_order_items I
ON I.product_id = P.id
WHERE
P.publish_date BETWEEN DATE_SUB( CURDATE( ) , INTERVAL 3 MONTH )
AND DATE_SUB( CURDATE( ) , INTERVAL 0 MONTH )
GROUP BY I.from_widget,
I.product_id
ORDER BY publish_date DESC ;
You could also make the query a nested one, if you don't like using SUM(quantity) many times:
SELECT
sum_quantity * buy_price AS ciro,
sum_quantity * list_price AS liste_ciro,
sum_quantity * widget_price AS vitrin_ciro,
tmp.*
FROM
( SELECT
SUM(I.quantity) AS sum_quantity,
I.from_widget,
COUNT(from_widget) AS order_count,
buy_price,
list_price,
widget_price,
P.*
FROM
tbl_products P
LEFT JOIN tbl_order_items I
ON I.product_id = P.id
WHERE
P.publish_date BETWEEN DATE_SUB( CURDATE( ) , INTERVAL 3 MONTH )
AND DATE_SUB( CURDATE( ) , INTERVAL 0 MONTH )
GROUP BY I.from_widget,
I.product_id
) AS tmp
ORDER BY publish_date DESC ;