如何将CURRENT_TIMESTAMP插入到PostGreSQL配置的Drupal安装中

I'm using drupal and a pgsql database, but after long searches I still can't figure out how to put a CURRENT_TIMESTAMP or now() into the database when inserting a row into a table. Putting now() on the default value of a column won't work, because drupal won't accept it on the database schema, so that's out of question.I'm using drupal and a pgsql database, but afte