Hi,

> > This should've been accepted, because the maximum key size is supposed
> > to be 256 bytes. But also, I think it might also depend on the page
> > size of your database. What is the page size that you defined?
>
> Page size makes no difference. It turns out that the collation
> has something to do with this. As soon as i dropped it from the domain
> i was able to create the constraint.
>
> Can anybody please explain why this is?

Before reinventing the wheel, does this help?

http://www.mers.com/IB_0245.HTML
http://www.mers.com/IBINDEXLENGHT.HTML

In short, the max index length also depends on the used
collation (whether it is a one or multi-byte collation),
and whether it is a compound index or not.

HTH,
Thomas.