Sql-server – SQL Server computed column select from another table

sql-serversql-server-2008

I'm not to sure what the best way to go about this is, so i'll describe what the end goal is, and if a computed column is the answer then please help me go that route, or perhaps a better route.

I have two tables:

Orders

OrderId
PackageId
MediaSpend
TotalAdViews (Computed column)

Packages

PackageId
BaseAdViews

Each order is assigned a package that comes with say 1,000 views, you can then buy more media spend to get more views. I wanted to create a column called TotalAdViews which would add BaseAdViews + MediaSpend. From my understanding if persistance is enabled the column won't need to recalculate every time it is queried, which could help performance.

How do I get a value from another table in my computed column? Or please suggest an alternate way of accomplishing my goal.

Best Solution

I know this answer comes two years late, but just to help anyone who googles and finds this post:

It is perfectly legal to define a user-defined function and use it as the computed value. This function may contain select statements from other tables.

CREATE FUNCTION dbo.getAdViews(@packageId int)
RETURNS INT
AS
BEGIN
    declare @bav int
    select @bav = BaseAdViews from Packages where PackageId = @packageId
    RETURN @bav
END

Then in your computed column, just use the expression dbo.getSumAdViews(PackageId)+MediaSpend as so:

CREATE TABLE [dbo].[Orders](
    [OrderId] [int] IDENTITY(1,1) NOT NULL,
    [PackageId] [int] NOT NULL,
    [MediaSpend] [int] NULL,
    [TotalAdViews] AS dbo.getAdViews(PackageId)+MediaSpend
) ON [PRIMARY]