index selection

i think this may have been posted previously, but here it goes. how does informix sql determine which index to use when executing a query? the problem we are having is we have a table that has several indexs which include a given column (lets say column_001); all but one are composite indexes as follows (as listed by the isql - tables - info - indexes ): create index idx1 on tab1 (columne_001,column_002); create index idx2 on tab1 (columne_001,column_009); create index idx3 on tab1 (columne_001); create index idx4 on tab1 (columne_001,column_005); when you execute the following query, the idx1 index is used: select * from tab1 where column_001 >= somevalue; i know that if i drop the idx1 and idx2 indexes isql will use the idx3 index. why is this? anyone else have this problem? has it been resolved in 5.01? ------------------------------------------------------------------------------ | . . Bob Baskett | ... ... Software Engineer, DBA | ..... ..... Business Systems Integration Group | .. ... .. Semiconductor Products Sector | . . . Mesa, AZ | | Motorola, Inc ------------------------------------------------------------------------------ Sun 690-MP Informix Versions: Online - 5.00.UC2 ISQL - 4.10.UD1 4GL-RDS- 4.10.UC1 ------------------------------------------------------------------------------