Question

I have a SQL Server 2008 database. This database has two related tables: Customer and Order. My tables look like this:

Customer
--------
ID
FirstName
LastName

Order
-----
ID
CustomerID
Amount
ShipDate

I need to delete all customers that do NOT have any orders. I cannot figure out the best way to do this. Can someone tell me how to do this? the NOT part is what keeps getting me. Originally I was using “IN” but it’s stumping me.

Thank you for your help!

Answer 1

Rather than using the IN operator, use a subquery and NOT EXISTS, something like:

DELETE Customers
FROM   Customers c
WHERE NOT EXISTS (
    SELECT 1
    FROM Orders o
    WHERE o.CustomerID = c.ID
)