Chapter 34. Triggers
   This chapter provides general information about writing trigger functions.
   Trigger functions can be written in most of the available procedural
   languages, including
   PL/pgSQL (Chapter 37),
   PL/Tcl (Chapter 38),
   PL/Perl (Chapter 39), and
   PL/Python (Chapter 40).
   After reading this chapter, you should consult the chapter for
   your favorite procedural language to find out the language-specific
   details of writing a trigger in it.
  
   It is also possible to write a trigger function in C, although
   most people find it easier to use one of the procedural languages.
   It is not currently possible to write a trigger function in the
   plain SQL function language.