In SQL Server, an empty string and a NULL value are not the same.

It can be shown by this:

create table #xxx (i int identity, a varchar(3))

declare @txt varchar(255)

set @txt = 'Question'

insert #xxx values ('')

select @txt = isnull (a, '?') from #xxx order by i

select @txt -- the result is '' (empty string)

insert #xxx values (null)

select @txt = isnull (a, '?') from #xxx order by i

select @txt -- the result is '?'

select @txt = a from #xxx order by i

select @txt -- the result is NULL

drop table #xxx

and this:

declare @var varchar(255)

set @var = ''

if @var is null select 'NULL' else select 'NOT NULL' -- the result is 'NOT NULL'

set @var = null

if @var is null select 'NULL' else select 'NOT NULL' -- the result is 'NULL'

As far as I know, NULLs and empty strings are equal in Oracle. But in SQL Server they are not.