Question

Given 2 tables

CustomerActivity
CustomerId, ActivityId, CreatedOnDate
1, 1, 8/1/2010
1, 2, 8/15/2010
2, 1, 7/24/2010
2, 2, 8/15/2010

TempUpdateTable
CustomerId, RecentActivityDate
1, NULL
2, NULL

How do I fill in the NULLs in TempUpdateTable using the CustomerActivity table?

My first attempt didn’t pan out:

UPDATE [TempUpdateTable]
SET RecentActivityDate = 
(SELECT MAX(CreatedOnDate) FROM CustomerActivity CA WHERE CA.CustomerId = CustomerId )

Thanks,

rod.

Answer 1

You can also try this:

UPDATE [TempUpdateTable] 
SET RecentActivityDate = Customers.MaxCreatedDate
FROM
(SELECT MAX(CreatedOnDate) as MaxCreatedDate, CA.CustomerId 
 FROM CustomerActivity CA WHERE CA.CustomerId = CustomerId 
 GROUP BY CA.CustomerId
) Customers
WHERE TempUpdateTable.CustomerId = Customers.CustomerId