Question

尝试在invoices表的UPDATE `invoices` SET invoices.`owes` = (`owes` - `paid`);表中创建新触发器之后

我收到一个错误消息，因为我已经在payments中更新了另一个触发器。（见下文）

我希望将现有触发器保留在下面，但是如何进行修改以将owes表中的owes更新为（paid-invoices）。

CREATE TRIGGER `after_payment_update` AFTER UPDATE 
   ON `payments`
     FOR EACH ROW UPDATE `invoices` 
     SET invoices.`paid` = (SELECT SUM(payments .`payment`) 
   FROM payments WHERE payments.`invoice` = invoices.`invoice`)

Answer 1

您不能创建第二个触发器，该触发器“触发”与另一个触发器相同的动作。相反，您将使用如下所示的DELIMITER $$语句，并在触发器中填充要执行的所有相关代码。

DELIMITER $$
CREATE TRIGGER after_update_payments
AFTER UPDATE ON payments
FOR EACH ROW BEGIN
UPDATE invoices
     SET NEW.paid = (SELECT SUM(payment) FROM payments WHERE invoice = NEW.invoice),
         NEW.owes = (owes -(SELECT SUM(payment) FROM payments WHERE invoice = NEW.invoice));
END $$
DELIMITER ;

您实际上在上面的触发器中不需要DELIMITER，因此，我将向您展示一个示例，其中需要使用它：

DELIMITER $$
CREATE TRIGGER after_update_payments
AFTER UPDATE ON payments
FOR EACH ROW BEGIN
  IF (some condition here) THEN
    UPDATE invoices
         SET NEW.paid = (SELECT SUM(payment) FROM payments WHERE invoice = NEW.invoice),
           NEW.owes = (owes -(SELECT SUM(payment) FROM payments WHERE invoice = NEW.invoice));
  END IF;
END $$
DELIMITER ;

作为一般规则，如果需要执行多个语句，这些语句的末尾需要使用;，则需要使用DELIMITER。如果这仍然没有道理，可以在here中找到有关分隔符的很好解释。

现在，顺便说一句，我认为这种方法不是最优的。在您遇到的情况下，我将要做的是创建一个合并这些表的视图。例如：

CREATE 
ALGORITHM = UNDEFINED 
DEFINER = `root`@`localhost` 
SQL SECURITY DEFINER
VIEW invoice_payments_view AS (

    SELECT 
    t1.*,
    SUM(t2.payment) as amount_paid,
    SUM(t2.owes - SUM(t2.payment)) as amount_owed
    FROM invoices t1
    JOIN payments t2 ON (t1.invoice=t2.invoice)
    GROUP BY t1.invoice
)

然后要访问amount_paid和amount_owed列，您只需查询以下内容：

SELECT invoice, amount_paid, amount_owed FROM invoice_payments_view 
WHERE invoice=1;

注意，我绝不是这个主题的专家，我只是向您展示如何应对这种情况。另外，我没有测试任何代码，因此您可能需要稍作修改。如果您有任何问题，请通知我，我可以进行更新。

mysql双触发一起两次更新

1 个答案: