Cascade delete question

Hi All,

Sorry if this is a double post.

Here is an example of my table which works

vid    vname        parentname
1    n1@test.com
2    n2@test.com    n1@test.com
3    n3@test.com    n1@test.com
4    n4@test.com    n1@test.com
5    n5@test.com    n3@test.com

So my simple cascade on delete states that if I delete a row whose vname
matches the parentname of any other delete those rows.

No problem this works great!

Now I have changed my data to

vid    vname        parentname
1    n1@test.com
2    n2@test.com    n1
3    n3@test.com    n1
4    n4@test.com    n1
5    n5@test.com    n3

Notice the parentname is a substring of the vname. I can get that
substring from a select query

select (substring(vname from 0 for position('@' in vname)) from table1

This query returns
vname
------
n1
n2
n3
n4
n5

Can I change my delete cascade constraint to do this substring query
instead of an exact match?

Is there anyway to accomplish what I need to do?

    Thanks

        Glenn MacGregor