Question

I have a like the one below that does a minus from another select. The problem I have is that if the second SELECT (the one to do minus with) returns NULL, the full query returns NULL even if the first query has values. Seems like MySQL thinks 1-NULL=NULL. How can I fix this?

SELECT round(sum(iv.`amount`)) - 
(
 SELECT round(sum(pay.`amount`)) amountSum

     FROM invoice iv
    LEFT JOIN invoiceFactoring ivf on ivf.invoiceID=iv.invoiceID 
    LEFT JOIN user systemuser ON (systemuser.userID=iv.ownerUserID)
    LEFT JOIN Payment pay ON (pay.`invoiceID`=iv.`invoiceID`)
     WHERE 
        (iv.invoiceStateID = 2 OR iv.invoiceStateID = 3) 
     AND 
    (ivf.`invoiceFactoringProcessID` = 7)
     AND     (pay.`paymentMethodID` = 1 OR pay.`paymentMethodID` = 2)
     AND systemuser.`groupID` = 1 
     AND iv.`disabled` <> 1 
     AND ivf.`invoiceExpiryDate` BETWEEN date_add(now(), INTERVAL - 28 DAY) AND date_add(now(), INTERVAL - 21 DAY)

)
    FROM invoice iv
    LEFT JOIN invoiceFactoring ivf on ivf.invoiceID=iv.invoiceID 
        LEFT JOIN user systemuser ON (systemuser.userID=iv.ownerUserID)
    WHERE 
    (iv.invoiceStateID = 2 OR iv.invoiceStateID = 3)
        AND 
    (ivf.`invoiceFactoringProcessID` = 7 or ivf.`invoiceFactoringProcessID`)
    AND systemuser.`groupID` = 1 
    AND iv.`disabled` <> 1   /* ta bort de som är inaktiva*/    
    AND ivf.`invoiceExpiryDate` BETWEEN date_add(now(), INTERVAL - 28 DAY) AND date_add(now(), INTERVAL - 21 DAY)

Answer 1

perhaps you can wrap the “inner” sql with an IFNULL

SELECT round(sum(iv.`amount`)) - 
IFNULL((
 SELECT round(sum(pay.`amount`)) amountSum
 FROM invoice iv
 LEFT JOIN invoiceFactoring ivf on ivf.invoiceID=iv.invoiceID 
 LEFT JOIN user systemuser ON (systemuser.userID=iv.ownerUserID)
 LEFT JOIN Payment pay ON (pay.`invoiceID`=iv.`invoiceID`)
 WHERE 
    (iv.invoiceStateID = 2 OR iv.invoiceStateID = 3) 
 AND 
    (ivf.`invoiceFactoringProcessID` = 7)
 AND     (pay.`paymentMethodID` = 1 OR pay.`paymentMethodID` = 2)
 AND systemuser.`groupID` = 1 
 AND iv.`disabled` <> 1 
 AND ivf.`invoiceExpiryDate` BETWEEN date_add(now(), INTERVAL - 28 DAY) 
 AND date_add(now(), INTERVAL - 21 DAY)
),0)

FROM invoice iv
LEFT JOIN invoiceFactoring ivf on ivf.invoiceID=iv.invoiceID 
    LEFT JOIN user systemuser ON (systemuser.userID=iv.ownerUserID)
WHERE 
(iv.invoiceStateID = 2 OR iv.invoiceStateID = 3)
    AND 
(ivf.`invoiceFactoringProcessID` = 7 or ivf.`invoiceFactoringProcessID`)
AND systemuser.`groupID` = 1 
AND iv.`disabled` <> 1   /* ta bort de som är inaktiva*/    
AND ivf.`invoiceExpiryDate` BETWEEN date_add(now(), INTERVAL - 28 DAY) AND date_add(now(), INTERVAL - 21 DAY)