Single‑table non‑sparse join and hash indexes inherit their statistics from their
underlying base table if the statistics have not been collected on the index itself.
This applies to single‑column statistics, single‑column‑index statistics, multicolumn
statistics, and multicolumn index statistics.
The following bullets summarize the available forms of statistical inheritance.
Underlying base tables can inherit the statistics from any single‑table non‑spare
join and hash indexes that reference them. In this case, it becomes possible to inherit
statistics from multiple qualified join and hash indexes.
Multicolumn statistics are inherited from an underlying base table by a single‑table
non‑sparse join index or hash index defined on it.
Partitioning columns can inherit the statistics from the system‑derived PARTITION
column, but only if the table is partitioned by a single‑column partitioning expression.
Bidirectional inheritance of statistics is implemented for single‑table non‑sparse
join indexes and hash indexes so that statistics collected on the single‑table non‑sparse
join or hash index are inherited by their underlying base table.
For this case, it is possible for there to be multiple qualified single‑table non‑sparse
join or hash indexes from which a base table could inherit statistics.
Bidirectional inheritance of statistics is implemented for PARTITION statistics, where
those statistics are inherited by the partitioning column of a row‑partitioned table
if the table is partitioned by a single‑column partitioning expression.
Bidirectional inheritance of statistics is not supported for PARTITION#Ln statistics.
The inheritance of statistics occurs when the derived statistics are built for the
base relations. All statistical inheritance is bidirectional.