$sql = "SELECT a.*,
SUM(IF(ISNULL(g.amount), NULL, IF(g.amount > 0, g.amount, 0))) AS amount,
u.user_id,
+ DATE(a.stamp) as stamp,
UNIX_TIMESTAMP(a.stamp) as unix_stamp
FROM ".TB_PREF."audit_trail AS a JOIN ".TB_PREF."users AS u
LEFT JOIN ".TB_PREF."gl_trans AS g ON (g.type_no=a.trans_no