You need to grant the REFERENCES privilege on the reference table to user2.
(See GRANT, Table Privileges section. Note that this cannot be granted to a role, must be granted to the user directly.)
Here's a demo:
SQL> create user user1 identified by user1;
User created.
SQL> grant create session, create table, unlimited tablespace to user1;
Grant succeeded.
SQL> create user user2 identified by user2;
User created.
SQL> grant create session, create table, unlimited tablespace to user2;
Grant succeeded.
SQL> create table user1.ref_table (id number primary key);
Table created.
SQL> insert into user1.ref_table values (1);
1 row created.
SQL> insert into user1.ref_table values (2);
1 row created.
SQL> commit;
Commit complete.
SQL> grant references on user1.ref_table to user2;
Grant succeeded.
SQL> connect user2/user2;
Connected.
SQL> create table oth_table (thing number, fk number);
Table created.
SQL> alter table oth_table add(constraint fk1 foreign key (fk)
2 references user1.ref_table on delete set null);
Table altered.
SQL> insert into oth_table values (42, 1);
1 row created.
SQL> insert into oth_table values (256, 2);
1 row created.
SQL> commit;
Commit complete.
SQL> connect user1/user1;
Connected.
SQL> delete from ref_table where id = 1;
1 row deleted.
SQL> commit;
Commit complete.
SQL> connect user2/user2;
Connected.
SQL> select * from oth_table;
THING FK
---------- ----------
42
256 2
If you want admin to do all the work, it'll need the CREATE ANY INDEX privilege, and you still need the REFERENCES grant to user2.
Here's how that could work:
SQL> create user user1 identified by user1;
User created.
SQL> create user user2 identified by user2;
User created.
SQL> create user admin identified by admin;
User created.
--- Grants
----------------
SQL> grant create session, create table, unlimited tablespace to user1;
Grant succeeded.
SQL> grant create session, create table, unlimited tablespace to user2;
Grant succeeded.
SQL> grant create session, create any table,
2 create any index, alter any table to admin;
Grant succeeded.
--- Create reference table as admin
----------------
SQL> connect admin/admin
Connected.
SQL> create table user1.ref_table (id number primary key);
Table created.
--- Do the "references" grant
----------------
SQL> connect / as sysdba
Connected.
SQL> grant references on user1.ref_table to user2;
Grant succeeded.
--- Create the second table as admin
----------------
SQL> connect admin/admin
Connected.
SQL> create table user2.oth_table (foo number, bar number);
Table created.
--- Add the constraint
----------------
SQL> alter table user2.oth_table add(constraint fk
2 foreign key (bar) references user1.ref_table(id)
3 on delete set null);
Table altered.
Your table is owned by USERGOD, but you are importing as DIGITALNOISE.
Yes, you have the IMPORT FULL DATABASE, but you are not doing a full import.
Using FROMUSER/TOUSER is one solution.
Performing a full import by adding the FULL=Y option is another.
Best Answer
That's exactly the kind of thing that oracle AUDIT is created for. The basic view is DBA_AUDIT_TRAIL, though there are several others. By defalt, Oracle has some auditing already enabled, but you may want to review and modify. Also you want to use the dbms_audit_mgmt package to move the audit tables out of the SYSTEM tablespace into their own dedicated tablespaces, as well as to do normal housekeeping. Details are in Part VI of the Security Guide.