I have no problem creating Function Based Indexes for non-unique indexes, such as IE indexes. However, I can't do the same for AK indexes (unique indexes). The "New" Button is not activated for enter Expression. Why?
That is by design because Oracle supports Function Based Indexes, but does not support Function Based Constraints. However, ERwin allows you to create Function Based Indexes for a Unique Index if you deselect 'Generate As Constraint'
Here are the steps to create a Function Based Index for a Unique Index (AK):
1: Create an Unique Index.
2: Uncheck the 'Generate As Constraint' for the index.
3: Click the empty field next to "1" under the Index Members Panel to activate the "New" Button.