T-SQL UPDATE query to fill NULL columns

I have the following query:

SELECT 
    Quotes.quoteID, Orders.orderID, Orders.invoiceID, 
    Quotes.parentOrderID AS QuoteParent, Orders.parentOrderID AS OrderParent
FROM 
    Quotes 
INNER JOIN 
    Orders ON Quotes.orderID = Orders.orderID

I need to fill all the OrderParent columns with valid (not null) values in QuoteParent column.

How do I write the UPDATE query?

>Solution :

How about:

UPDATE o
SET parentOrderID = q.parentOrderID
FROM dbo.Orders o
INNER JOIN Quotes q ON o.OrdersID = q.OrderID
WHERE o.parentOrderID IS NULL
  AND q.parentOrderID IS NOT NULL