I tried again and got the following:

This operation is not defined for system tables.
unsuccessful metadata update.
STORE RDB$INDICES failed.
attempt to store duplicate value (visible to active transactions) in unique
index "RDB$INDEX_5".

Script used was:

alter table ATTENDANCE
add constraint FK_ATTENDANCE
foreign key (PERSONID)
references PEOPLE(PERSONID)
on delete CASCADE
on update CASCADE
using index PERSON_IDX



_________________________________________
Don Gollahon
dlgllhn@...
ICQ#: 115831669
"What in Eternity does it matter?"
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