insert语句是否与另一个表中的数据匹配

CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY,
    CustomerName VARCHAR(255)
);

CREATE TABLE Orders (
    OrderID INT PRIMARY KEY,
    CustomerID INT,
    OrderDate DATE,
    FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

CREATE TRIGGER trg_CheckCustomerBeforeInsert
BEFORE INSERT ON Orders
FOR EACH ROW
BEGIN
    DECLARE customer_exists INT;
    SELECT COUNT(*) INTO customer_exists FROM Customers WHERE CustomerID = NEW.CustomerID;
    IF customer_exists = 0 THEN
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Customer does not exist';
    END IF;
END;

DELIMITER //
CREATE PROCEDURE InsertOrder(IN p_CustomerID INT, IN p_OrderDate DATE)
BEGIN
    DECLARE customer_exists INT;
    SELECT COUNT(*) INTO customer_exists FROM Customers WHERE CustomerID = p_CustomerID;
    IF customer_exists > 0 THEN
        INSERT INTO Orders (CustomerID, OrderDate) VALUES (p_CustomerID, p_OrderDate);
    ELSE
        SIGNAL SQLSTATE '45000' SET MESSAGE_TEXT = 'Customer does not exist';
    END IF;
END //
DELIMITER ;