SQL Server computed column select from another table

Question

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

Answer 1

You won't be able to use columns from another table within a computed column expression. This is an extract from the MSDN documentation.

A computed column is computed from an expression that can use other columns in the same table.

You mentioned that your motivation for using a computed column was to increase performance. There are a lot of restrictions but an indexed view might add value here.

Answer 2

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]

Answer 3

if it is only for display purposes,why not create a view..

select <<add other columns you need>> mediaspend+basicadviews as totaladviews
from 
orders o
join
packages p
on p.packageid=o.orderid