Preventing Indexes on Foreign Keys

Hi everyone, I have several tables that I create with Foreign Keys on columns, but I do NOT want Informix to automatically put an index on some of these columns. Is there a way to prevent this? In addition, can anyone tell me why Informix does this? I definitely see situations where an index on a FK would be detrimental to performance. For example, assume a table has 3 columns: site_id, date_time, data1, where site_id is a FK with possible values of 1 to 20. Now assume a new row is inserted into this table every 10 seconds 24 hours a day 7 days a week, where the table on the average contains 2 million rows. Now assume that all queries have the following form: SELECT date_time, data1 FROM table WHERE date_time BETWEEN "1998-03-10 00:00:00" AND "1998-03-10 01:00:00" AND site_id = 1 ORDER BY date_time; From a performance view: An index(date_time) or an index(date_time, site_id) would drastically improve performance, but an index only on site_id will not give a big improvement, since the selectiveness of the index is only 1/20. Therefore, performance would be degraded for all the inserts and the select performance would increase slightly. My thoughts on this would be to drop the index on the site_id, which is the FK, and put one index(date_time, site_id). ie. I don't want Informix to automatically put an index on the site_id, the FK. Are there any other opinions out there? I'm using HP-UX 10.10 with Informix Online 7.13.UC5. TIA, Jim Koermer USCG Loran Support Unit, Wildwood, NJ. jkoermer@lsu.uscg.mil