MySQL 3.23.53 и MySQL 4.0.22 баг или фича?

[berkut]

MySQL 3.23.53 и MySQL 4.0.22 баг или фича?

есть две таблицы

CREATE TABLE xaffilate_partners (
 ........................................
  amount float(5,2) unsigned NOT NULL default '0.00',
 ........................................ 
)

и

CREATE TABLE xaffilate_paidhistory (
.................................................
  amount float(5,2) unsigned NOT NULL default '0.00'
) TYPE=MyISAM;

создаю 3-ю таблицу

CREATE TABLE xaffilate_temp
SELECT id, xaffilate_partners.amount, login, wmz,
            IF ( SUM(xaffilate_paidhistory.amount) IS NOT NULL, SUM(xaffilate_paidhistory.amount), 0.00 )
            AS paided
            FROM xaffilate_partners
            LEFT JOIN `xaffilate_paidhistory` ON ( xaffilate_paidhistory.partner_id = xaffilate_partners.id )
            GROUP BY id

в итоге, если SUM(xaffilate_paidhistory.amount) is null в xaffilate_temp.paided записывется NULL, а не 0.00 в
MySQL 4.0.22
А в MySQL 3.23.53 xaffilate_temp.paided записывется 0.00. В 3.23.53 даже запрос типа

CREATE TABLE xaffilate_temp
SELECT id, xaffilate_partners.amount, login, wmz,
           SUM(xaffilate_paidhistory.amount)  AS paided
            FROM xaffilate_partners
            LEFT JOIN `xaffilate_paidhistory` ON ( xaffilate_paidhistory.partner_id = xaffilate_partners.id )
            GROUP BY id

пишет в xaffilate_temp.paided 0.00(если сумма =null)
Как заставить 4.0.22 писать 0.00?