15.10 - Statistical Inheritance by Hash and Join Indexes - Teradata Database

Teradata Database SQL Request and Transaction Processing

prodname
Teradata Database
vrm_release
15.10
category
Programming Reference
User Guide
featnum
B035-1142-151K

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.