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

david-rowley · david-rowley · commit 59634df871a4 · 2023-06-22T12:51:36.000+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
@@ -125,6 +125,12 @@ CREATE STATISTICS [ IF NOT EXISTS ] <replaceable class="parameter">statistics_na
    reading it.  Once created, however, the ownership of the statistics
    object is independent of the underlying table(s).
   </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">
