Search notes:

Oracle: Extended statistics

There are two types of extended statitics:

Multicolumn statistics	The focus is to gather statistics for sets of columns with correlating values (for example `city` and `state`, or `age` and `income`, or `temperature` and `ice_cream_sales` etc.)
Expression Statistics

See also

dba_stat_extensions

dbms_stats.create_extended_stats

The (undocumented) init parameters

_optimizer_extended_cursor_sharing
_optimizer_extended_cursor_sharing_rel
_optimizer_extended_stats_usage_control
_optimizer_extend_jppd_view_types

function-based index

MOS Note 1489505.1: How Does Using Expression Statistics Differ from Using a Function-Based Index?