doc: mention trigger helper functions in CREATE TRIGGER docs

Reported-by: petermpallesen@gmail.com
Discussion: https://postgr.es/m/159195294959.673.5752624528747900508@wrigleys.postgresql.org

Backpatch-through: 9.5

diff --git a/doc/src/sgml/ref/create_trigger.sgml b/doc/src/sgml/ref/create_trigger.sgml
index 91293b7ca17e84cfcfd8a86a8719ec018ec74271..576e27f4dcce9eb3c6507356a8ce133fae24db0a 100644 (file)
--- a/doc/src/sgml/ref/create_trigger.sgml
+++ b/doc/src/sgml/ref/create_trigger.sgml
@@ -447,6 +447,12 @@ UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</
    value did not change.
   </para>
 
+  <para>
+   There are a few built-in trigger functions that can be used to
+   solve common problems without having to write your own trigger code;
+   see <xref linkend="functions-trigger">.
+  </para>
+
   <para>
    In a <literal>BEFORE</> trigger, the <literal>WHEN</> condition is
    evaluated just before the function is or would be executed, so using