Question

我有一些具有相同字段值的表，不能重复。我决定在制作INSERT时创造价值。触发器获取最大值并添加1.但在SELECT MAX(account_number) AS last_account_number INTO last_account_number FROM companies; last_account_number之后始终为null，但值为，并且外部请求触发器本身运行顺利。

CREATE TRIGGER    generate_account_number_for_companies
before insert
ON companies FOR EACH ROW

    BEGIN
    DECLARE account_number INT;
    DECLARE last_account_number INT;

    SELECT MAX(account_number) AS last_account_number INTO last_account_number FROM companies;

    IF last_account_number is null THEN
        SET New.account_number = 10000000;
    ELSE
        SET New.account_number = last_account_number + 1;
    END IF;
END

Answer 1

首先，您的AS last_account_number声明中不需要SELECT ... INTO部分。其次，您当前的companies表中是否有数据，或者它是否为空？如果它不为空，请尝试修改语句以排除NULL值：

SELECT MAX(account_number) INTO last_account_number FROM companies WHERE account_number IS NOT NULL;

如果coalesce返回，您还可以在其中添加0以将其设置为NULL。

SELECT COALESCE(MAX(account_number), 0) INTO last_account_number FROM companies WHERE account_number IS NOT NULL;

您还要声明一个与您尝试选择的列名称相同的变量，从触发器中删除该行：DECLARE account_number INT;。

在触发器中，未设置选择的结果

1 个答案: