Performing an UPDATE with Union in SQL

Question

If I were to have these three tables (just an example in order to learn UNION, these are not real tables):

Tables with their columns:

Customer: 
id | name        | order_status

Order_Web:
id | customer_id | order_filled

Order:
id | customer_id | order_filled

And I wanted to update order_status in the Customer table when there is a order filled in either the Order_Web table or the Order table for that customer using Union:

UPDATE c
SET c.order_status = 1
FROM Customer AS c
INNER JOIN Order_Web As ow
      ON c.id = ow.customer_id
WHERE ow.order_filled = 1

UPDATE c
SET c.order_status = 1
FROM Customer AS c
INNER JOIN Order As o
      ON c.id = o.customer_id
WHERE o.order_filled = 1

How can I combine these two updates using a Union on order_web and order?

Using Microsoft SQL Server Management Studio

Answer 1

You do not need a UNION for that - replacing an inner join with a pair of outer ones should do it:

UPDATE c
SET c.order_status = 1
FROM Customer AS c
LEFT OUTER JOIN Order_Web As ow ON c.id = ow.customer_id
LEFT OUTER JOIN Order As o ON c.id = o.customer_id
WHERE ow.order_filled = 1 OR o.order_filled = 1

You could also use a WHERE EXISTS, like this:

UPDATE c
SET c.order_status = 1
FROM Customer AS c
WHERE EXISTS (
    SELECT 1 FROM Order_Web As ow WHERE c.id = ow.customer_id AND ow.order_filled = 1 
) OR EXISTS (
    SELECT 1 FROM Order As o WHERE c.id = o.customer_id AND o.order_filled = 1
)

If you must use UNION, you can do it as follows:

UPDATE c
SET c.order_status = 1
FROM Customer AS c
WHERE c.id in (
        SELECT ow.id FROM Order_Web As ow WHERE ow.order_filled = 1 
    UNION
        SELECT o.id FROM Order As o WHERE o.order_filled = 1
)

or the same one with a JOIN:

UPDATE c
SET c.order_status = 1
FROM Customer AS c
JOIN (
        SELECT ow.id AS id FROM Order_Web As ow WHERE ow.order_filled = 1 
    UNION
        SELECT o.id AS id FROM Order As o WHERE o.order_filled = 1
) AS ids ON ids.id = c.id