Question

I have a table with following scehma

CREATE TABLE MyTable  
(  
  ID                INTEGER DEFAULT(1,1),  
  FirstIdentifier   INTEGER NULL,  
  SecondIdentifier  INTEGER NULL,  
--.... some other fields .....  
) 

Now each of FirstIdentifier & SecondIdentifier isunique but NULLable. I want to put a unique constraint on each of this column but cannot do it because its NULLable and can have two rows with NULL values that will fail that unique constraints. Any ideas of how can I address it on schema level?

Answer 1

You can use a filtered index as a unique constraint.

create unique index ix_FirstIdentifier on MyTable(FirstIdentifier) 
  where FirstIdentifier is not null