Why does the optimizer do this ? uhmmmmmm

Something I noticed with Set Explain; Index: Unique Index: location_pk, bldg_no, div_number QUERY: ------ select location_pk, loc_type from raw_inventory where location_pk =311006511 Estimated Cost: 2 Estimated # of Rows Returned: 3 1) informix.raw_inventory: SEQUENTIAL SCAN Filters: informix.raw_inventory.location_pk = 311006511 QUERY: ------ select location_pk from raw_inventory where location_pk = 311006511 Estimated Cost: 1 Estimated # of Rows Returned: 3 1) informix.raw_inventory: INDEX PATH (1) Index Keys: location_pk bldg_no div_number (Key-Only) Lower Index Filter: informix.raw_inventory.location_pk = 311006511 ==================================================================== If you are using a composite index and only use the first part of the index in your where clause. You will get a performance hit if you select anything other than that column. If the where clause included the entire key, you can select other cohe where clause included the entire key, you can select other columns without any peformance delays.