it seems you cannot reference a udf in a computed col from any other database not just tempdb. You would have to create the function in tempdb.

i.e - this does not work either:

use pubs

go

create function udf_isblank(@n varchar(20) = null, @ret varchar(20))

returns varchar(20)

as

begin

declare @NULL int

set @NULL =  case when isnull(@n,'') = '' then @ret

  else @n

  end

return @NULL

end

select pubs.dbo.udf_isblank('',0)

use northwind

go

--drop table test

create table test(

val int,

result as pubs.dbo.udf_isblank(val,0)

)

insert test (val) values(5)

insert test (val) values('')

insert test (val) values(null)

select * from test