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 55d53445c4d96a74768e7f4f8ac5c2a608816f32..86733b0116c276c239cf57ba53bcd34c1d2d0edf 100644 (file)
--- a/doc/src/sgml/ref/create_trigger.sgml
+++ b/doc/src/sgml/ref/create_trigger.sgml
@@ -455,6 +455,12 @@ 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</literal> trigger, the <literal>WHEN</literal> condition is
    evaluated just before the function is or would be executed, so using