SQL Server：标量函数不返回任何内容，但它应该返回 INT

Question

这是我的功能：

CREATE FUNCTION fu_order_customer_adress (@customer_ID INT)
RETURNS INT AS
    BEGIN
        RETURN (
            SELECT c.adress_ID FROM customers AS c
            JOIN orders AS o ON (c.customer_ID = o.customer_ID)
            WHERE c.customer_ID = @customer_ID)
    END

用于表orders的AFTER INSERT触发器，其结构如下（不含不重要的列）：

orders (order_ID INT, customer_ID INT, employee_ID)

order_ID是主键，其他列是外键。

触发器如下所示：

CREATE TRIGGER tr_orders_insert ON orders
AFTER INSERT 
AS
BEGIN
    DECLARE @order_ID INT = (SELECT order_ID FROM INSERTED);
    DECLARE @customer_ID INT = (SELECT customer_ID FROM INSERTED);

    UPDATE orders
    SET adress_ID = (SELECT dbo.fu_order_customer_adress(@customer_ID))
    WHERE order_ID = @order_ID;
END

以下插入已编号，以便稍后轻松指出。

(1) 这适用于具有不同 customer_ID 的插入：

INSERT INTO orders(customer_ID, employee_ID) 
VALUES (1, 1)

INSERT INTO orders(customer_ID, employee_ID) 
VALUES (2, 2)

(2) 但是当插入已经使用customer_ID的订单时，插入会以错误结束：

INSERT INTO orders(customer_ID, employee_ID) 
VALUES (1, 2)

我发现这是由触发器中使用的函数引起的，因为在这种情况下它什么也不返回。

我尝试将函数中使用的SELECT function 和SELECT 放入触发器中：

CREATE TRIGGER tr_orders_insert ON objednavka
AFTER INSERT 
AS
BEGIN
    DECLARE @order_ID INT = (SELECT order_ID FROM INSERTED);
    DECLARE @customer_ID INT = (SELECT customer_ID FROM INSERTED);

    SELECT c.adress_ID 
    FROM customers AS c
    JOIN orders AS o ON (c.customer_ID = o.customer_ID)
    WHERE c.customer_ID = @customer_ID)

    SELECT dbo.fu_order_customer_adress(@customer_ID)

    UPDATE orders
    SET adress_ID = (SELECT dbo.fu_order_customer_adress(@customer_ID))
    WHERE order_ID = @order_ID;
END

In (1) 都是SELECT 结果相同。

In (2) 是SELECT 结果正常，但SELECT function 什么也不返回。

我不明白出了什么问题...感谢您的帮助！

Answer 1

对于你这个简单的触发器，我认为你不需要这个性能杀手标量函数，你可以简单地执行以下操作，而无需使用任何标量函数，只需将表与插入的表连接起来。

此外，您的触发器中的逻辑存在重大问题，它仅适用于单个插入，如果您的 Orders 表中有多个插入，它将失败。一种更安全、性能更高效的方法是......

CREATE TRIGGER tr_orders_insert ON orders
AFTER INSERT AS
BEGIN
  SET NOCOUNT ON;

    UPDATE O
       SET O.adress_ID = C.adress_ID
    FROM orders O 
    INNER JOIN inserted  AS I   ON O.order_ID    = I.order_ID 
    INNER JOIN customers AS c   ON C.customer_ID = I.customer_ID         

END