Doc: mention that extended stats aren't used for joins

david-rowley · david-rowley · commit 8145b5e138c7 · 2023-06-22T12:47:53.000+12:00
Statistics defined by the CREATE STATISTICS command are only used to assist with the selectivity estimations of base relations, never for joins. Here we mention this fact in the notes section of the CREATE STATISTICS command. Discussion: https://postgr.es/m/CAApHDvrMuVgDOrmg_EtFDZ=AOovq6EsJNnHH1ddyZ8EqL4yzMw@mail.gmail.com Backpatch-through: 11
diff --git a/doc/src/sgml/ref/create_statistics.sgml b/doc/src/sgml/ref/create_statistics.sgml
@@ -167,6 +167,12 @@ CREATE STATISTICS [ IF NOT EXISTS ] <replaceable class="parameter">statistics_na
    maintenance. Expression statistics are built automatically for each
    expression in the statistics object definition.
   </para>
+
+  <para>
+   Extended statistics are not currently used by the planner for selectivity
+   estimations made for table joins.  This limitation will likely be removed
+   in a future version of <productname>PostgreSQL</productname>.
+  </para>
  </refsect1>
 
  <refsect1 id="sql-createstatistics-examples">
