...e provare a cercare un po' con google ?...

http://www.dsf.unica.it/~andrea/L5/2004-12-13/pl1.pdf
http://www.postgresql.org/docs/curre...l-trigger.html
http://www.faqs.org/docs/ppbook/x20655.htm
http://jamesthornton.com/postgres/7....l-trigger.html