Help check constraint no duplicate record

[AnnYH]

Hi, Everyone:

Is it any way can help me to solve my question?

In my main table, I have primary key PID. And another column is WBNUM( data type: nvarchar , allowed Null).

For WBNUM, I need this column can be null, after it is entered a data, they are not allowed to be duplicate.

What can I do for this? I try creating a Unique Constraint, but you must ensure that at most one row will have a null.

I must allowed more than one row to be null.

Any idea, please help. Thanks a lot

Ann

 

[SQLSister]

Do it with a trigger instead of a constraint. Use an if statement in the trigger to check if it is null and then do the check only if it is not.