On 20th of November Tom Lane committed patch by Takahiro Itagaki which adds interesting functionality:
ADD a WHEN clause TO CREATE TRIGGER, allowing a BOOLEAN expression TO be checked TO determine whether the TRIGGER should be fired. FOR BEFORE triggers this IS mostly a matter OF spec compliance; but FOR AFTER triggers it can provide a noticeable performance improvement, since queuing OF a DEFERRED TRIGGER event AND re-fetching OF the ROW(s) at END OF statement can be short-circuited IF the TRIGGER does NOT need TO be fired. Takahiro Itagaki, reviewed BY KaiGai Kohei.