Subject Unique (?) constraint
Author chrisacron
Hi All

Please help a FireBird newbie. I want to create a constraint that
allows duplicate null (or blank fields) but unique if there are
characters in it.

In other words as long as the user leaves the field blank, he can have
many records that are blank. When he enters a value into the field it
should make sure that that value is unique.

Is this possible (and how) ?