Index Scans: Key-First
select count(e)from mytable
Estimated # of Rows Returned: 1
1) informix.mytable: INDEX PATH
Filters: informix.mytable.d = 'Y'
(1) Index Keys: a b c d (Key-First) (Serial, fragments: ALL)
Lower Index Filter: (informix.mytable.a = 1 AND informix.mytable.b = 1 )