Hi Maureen, You write you checked the master tables. If the MVIEW has joins it is still possible that we find duplicate keys in the MVIEW even though the master tables are ok, An index create points to the MVIEW rather than to the master tables. Thus a unique index on the MVIEW should create your issues. How about creating your MVIEW as prebuild table and check for anything fishy? You can try as well to build the MVIEW on top of the prebuild table and see it that gives you a work around. Thanks Lothar ----Ursprüngliche Nachricht---- Von : maureen.english@xxxxxxxxxx Datum : 15/12/2014 - 11:17 (GMT) An : oracle-l@xxxxxxxxxxxxx Betreff : ORA-01452 when creating a materialized view Hi, I have what seems to me to be a very strange problem. We just migrated our reporting instance from 10.2.0.4 to 11.2.0.2 (yes, I know we need to upgrade, but hardware issues are preventing that at the moment). After the migration, most things seem to be working, all the materialized views got created without errors as far as I can tell. For all of the materialized views that are done as fast refreshes, I need to do a complete refresh before we can do the fast refreshes again because we use the refresh with rowid method. I ran into a problem with 2 materialized views where I got the following error. ORA-01452: cannot CREATE UNIQUE INDEX; duplicate keys found when recreating a materialized view This happens on the create statement, after I dropped the materialized view. We checked the tables in the master database and they don't have any problems - my coworker ran analyze on them. I do have a ticket in with Oracle, but thought that maybe someone has seen this before and can offer a suggestion. I'm concerned that since this is a production reporting instance, I'll have users who will be unable to get their data tomorrow morning.... - Maureen