MYSQL Sum Query with IF Condition

How about this?

SUM(IF(PaymentType = "credit card", totalamount, 0)) AS CreditCardTotal

Try with a CASE in this way :

SUM(CASE 
    WHEN PaymentType = "credit card" 
    THEN TotalAmount 
    ELSE 0 
END) AS CreditCardTotal,

Should give what you are looking for ...