Oracle视图ORA-00907：缺少右括号

Question

SELECT 
    SALE.SaleID,
    SALE.SaleDate,
    CUSTOMER.CustomerID, 
    FIRSTNAMEFIRST(Customer.FirstName, Customer.LastName),
    SALE_ITEM.SaleItemID,
    SALE_ITEM.ItemID,
    ITEM.ItemDescription, 
    ITEM.ItemPrice
FROM CUSTOMER
INNER JOIN SALE ON CUSTOMER.CustomerID = SALE.CustomerID
INNER JOIN SALE_ITEM ON SALE.SaleID = SALE_ITEM.SaleID
INNER JOIN ITEM ON SALE_ITEM.ITEMID = ITEM.ItemID

即使我测试视图它会显示正确的查询结果，但我无法弄清楚错误ORA-00907。

功能定义

CREATE OR REPLACE FUNCTION FIRSTNAMEFIRST 
    ( FIRSTNAME IN VARCHAR2, LASTNAME IN VARCHAR2 ) RETURN VARCHAR2
AS 
BEGIN
    RETURN TRIM(FIRSTNAME) || ', ' || TRIM(LASTNAME);
END;

Answer 1

在FIRSTNAMEFIRST(Customer.FirstName, Customer.LastName)之后添加AS FullName之后，它工作了。对不起，如果我没有包含足够的信息，谢谢。