-- WHEN credit >= $gift THEN (credit+$gift WHERE email = '$email')
-- ELSE 'credit dont enought'
-- credit= if(credit <= $gift , credit - $gift  ,null)
-- WHERE id = '$user_id';
-- UPDATE user SET credit=credit+$gift WHERE email = '$email';
-- UPDATE user SET 
-- credit=(CASE 
--             WHEN dd THEN credit = credit+$gift END) 
-- WHERE email = '$email';