miserable performance of union as view

I'm now using informix 7.30 UC5 on AIX. I was waiting for the feature union in a view for quite a long time! And then this bad awakening! Assume you have a table DATA with about 10.000 records, heavily referenced by another table BIG with 200.000 - 500.000 rows. Sometimes it is necessary to reorganize the DATA table, which means deleting all duplicates of rows which are logical equal items (but holding different data). DATA is maintained by users, but filled with rows via data-transmission too - so we can't avoid logical duplicates in advance. Well, when reorganizing DATA it is not possible to update BIG. So we sat up a table LINK which hold the real_key and the pseudo_key. To resolve any key, wether real or not I create a view DATA_VIEW as: select * from DATA union allselect LINK.pseudo_key key,.... from DATA,LINK where DATA.key = LINK.real_key selecting via the view (select * from data_view where key=123) is awful slow - althogh the statement (select * from data union ...) itself is pretty fast!! Why? Can I do anything to improve performance? I added the 'union all' to tell the database-server there is no need to check for duplicate rows! Thank you very much for your help Peter Weigert