Working with Nulls

Question

I have the below query which returns what products are on what orderID.

SELECT  P.Name,
STUFF   (( SELECT ' | ' +  CONVERT(VARCHAR(22) , SOD.SalesOrderID)
        FROM Sales.SalesOrderDetail SOD
        WHERE
        P.ProductID = SOD.ProductID 
        FOR XML PATH ('')
        ), 1, 1, '')
        as Orders
FROM Production.Product P

However, I am having trouble with the 'Nulls'. I've tried isnull is different parts of the code as well as a case statement but can't seem to figure where it would go.

If anyone can give me any help that would be great.

Answer 1

My guess is that the problematic NULL s are in SOD.SalesOrderId .

One way to handle them is by filtering them out:

SELECT  P.Name,
STUFF   (( SELECT ' | ' +  CONVERT(VARCHAR(22) , SOD.SalesOrderID)
        FROM Sales.SalesOrderDetail SOD
        WHERE
        P.ProductID = SOD.ProductID and SOD.SalesOrderId is not null
        FOR XML PATH ('')
        ), 1, 1, '')
        as Orders
FROM Production.Product P

Another way is to convert them to some acceptable representation:

SELECT  P.Name,
STUFF   (( SELECT ' | ' +  coalesce(CONVERT(VARCHAR(22) , SOD.SalesOrderID), '<NULL>')
        FROM Sales.SalesOrderDetail SOD
        WHERE
        P.ProductID = SOD.ProductID 
        FOR XML PATH ('')
        ), 1, 1, '')
        as Orders
FROM Production.Product P

EDIT:

The NULL s are being returned because there is no match in SalesOrderDetail for the records. What would you want returned in this case?

To find those products:

select p.*
from Production.Product p left outer join
     Sales.SalesOrderDetail sod
     on p.ProductID = SOD.ProductID
where sod.ProductId is null;

If you want to filter them out, then use a subquery:

select t.*
from (<either of the above queries>) t
where t.Orders is not NULL

EDIT II:

If you want blanks to be returned, then wrap coalesce() around the value:

SELECT  P.Name,
coalesce(STUFF   (( SELECT ' | ' +  CONVERT(VARCHAR(22) , SOD.SalesOrderID)
        FROM Sales.SalesOrderDetail SOD
        WHERE
        P.ProductID = SOD.ProductID 
        FOR XML PATH ('')
        ), 1, 1, ''), '')
        as Orders
FROM Production.Product P