I suggest to add some kind of reference to stats expressions here.
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
<sect2 id="vacuum-for-statistics">
<title>Updating Planner Statistics</title>
<indexterm zone="vacuum-for-statistics">
<primary>statistics</primary>
<secondary>of the planner</secondary>
</indexterm>
[...]
@@ -330,10 +330,12 @@
<para>
Also, by default there is limited information available about
- the selectivity of functions. However, if you create an expression
+ the selectivity of functions. However, if you create a statistics
+ expression or an expression
index that uses a function call, useful statistics will be
gathered about the function, which can greatly improve query
plans that use the expression index.
--
Justin
