SQL Server all(select …) is null

Question

I search but i cannot find anything about it. I need SQL server query like

select t1.x 
 from @tablename as t1 
 where all
   (select t2.y from @tablename as t2 where t1.x=t2.x) is null

@tablename 's are same

But I can't use all(select ...) is null part of query.

Thanks.

Answer 1

Do you want not exists ?

select t1.x 
from @tablename as t1 
where not exists (select t2.y from @tablename as t2 where t1.x = t2.x) 

This tests that there are no matching values.

Or, perhaps,

select t1.x 
from @tablename t1 
where not exists (select 1
                  from @tablename as t2
                  where t1.x = t2.x and t2.y is not null
                 ) ;

This tests that any matching value has NULL for y .