在触发器中使用 If_Else 时出错

Question

请参考下图

我想在Ongoing_Fees 表上创建一个After Insert 触发器，用于更新VAT 表。但是在将数据插入增值税表之前，它应该检查特定Portfolio 的VAT 字段是否为true。 Ongoing_Fees 表拥有foreign key 对Portfolio 表的访问权限，因此可以访问相关的投资组合。

以下是我尝试过的

DELIMITER $$
CREATE TRIGGER `Ongoing_Fees_AINS` AFTER INSERT ON `Ongoing_Fees` FOR EACH ROW
BEGIN
DECLARE `vat` Boolean;
`vat` = SELECT VAT from Portfolio WHERE Portfolio.idPortfolio = New.idPortfolio;

IF (`vat` == true) THEN
    INSERT INTO VAT VALUES (100, current_Timestamp, New.idPortfolio, New.idOngoing_Fees)
END;

当然，它有一个错误

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '= SELECT VAT from Portfolio WHERE Portfolio.idPortfolio = New.idPortfolio;

Answer 1

试试：

DELIMITER $$

CREATE TRIGGER `Ongoing_Fees_AINS` AFTER INSERT ON `Ongoing_Fees`
FOR EACH ROW
BEGIN
  DECLARE `_vat` BOOL;
  SET `_vat` := (SELECT `VAT` FROM `Portfolio` WHERE `Portfolio`.`idPortfolio` = NEW.`idPortfolio`);    
  IF (`_vat` = TRUE) THEN
    INSERT INTO `VAT` (
         `Amount`,
         `current_timestamp`,
         `Portfolio_idPortfolio`,
         `Ongoing_Fees_idOngoing`
    )
    VALUES (
         100,
         CURRENT_TIMESTAMP(),
         NEW.`idPortfolio`,
         NEW.`idOngoing_Fees`
    );
  END IF;
END$$

DELIMITER ;

更短的版本：

DELIMITER $$

CREATE TRIGGER `Ongoing_Fees_AINS` AFTER INSERT ON `Ongoing_Fees`
FOR EACH ROW
BEGIN
    INSERT INTO `VAT` (
         `Amount`,
         `current_timestamp`,
         `Portfolio_idPortfolio`,
         `Ongoing_Fees_idOngoing`
    )
    SELECT
         100,
         CURRENT_TIMESTAMP(),
         NEW.`idPortfolio`,
         NEW.`idOngoing_Fees`
    FROM
         DUAL
    WHERE
         TRUE = (SELECT
                      `VAT`
                 FROM
                      `Portfolio`
                 WHERE
                      `Portfolio`.`idPortfolio` = NEW.`idPortfolio`
                );
END$$

DELIMITER ;