informix

We are in need of Informix expertise in two areas: 1) query optimization and the use of indexes, and 2) performance tuning using self-joins and outer joins. 1) We have a query that should use an index, but doesn't. When a second index is added to the table, the query now recognizes and uses the first index while ignoring the second. Does anyone have suggestions as to why this is happening? 2) We have a view that performs a self-outer join. Example: select a.part, b.part, c.part from failures a, outer failures b, outer failures c where a.failnum = b.failnum and a.failnum = c.failnum and a.code = "OPEN" and b.code = "ASSESSED" and c.code = "REPAIRED" Does anyone have experience with this type of query? Any performance tuning tips, specifically in the area of temp table use or indexes on the underlying tables of a view? Thanks, Gary J.