UNIQUE constraint controlled by a bit column

Question

I have a table, something like

FieldsOnForms(
 FieldID int (FK_Fields)
 FormID int (FK_Forms)
 isDeleted bit
)

The pair (FieldID,FormID) s

Answer 1

You can have a unique index, using the SQL Server 2008 filtered indexes feature, or you can apply a UNIQUE index against a view (poor man's filtered index, works against earlier versions), but you cannot have a UNIQUE constraint such as you've described.

An example of the filtered index:

 CREATE UNIQUE NONCLUSTERED INDEX IX_FieldsOnForms_NonDeletedUnique ON FieldsOnForms (FieldID,FormID) WHERE isDeleted=0