I've created a unique constraint for a field ( varchar(20) ) the field accepts null values, however, when I try to insert more than one row with a null value in this field, I get an error stating that I'm violating the constraint, from what I read I thought you could have as many NULL values as you wanted, and the constraint only applied to non-null values, did I misundesrstand this or am I missing something else?, I'm using SQL Server 7.0, TIA