如何在删除触发器后更新 table 中的行

Question

我有一个tablecountry_group

+------+----------+--------+
| code | group_id | weight |
+------+----------+--------+
| me   | 1        | 50.00  |
+------+----------+--------+
| me   | 2        | 10.00  |
+------+----------+--------+
| me   | 3        | 40.00  |
+------+----------+--------+

对我来说，每个国家/地区的列权重总和为 100 非常重要。我想在这里做的是，当我删除其中一行时，我需要更改该国家/地区的权重值，以便所有的总和该国家/地区的权重仍然是 100。我想为此在我的数据库中设置触发器。

例如，如果我删除权重为 10.00 的行，那么 table 应该如下所示：

+------+----------+--------+
| code | group_id | weight |
+------+----------+--------+
| me   | 1        | 55.00  |
+------+----------+--------+
| me   | 3        | 45.00  |
+------+----------+--------+

所以这是我的触发器：

CREATE DEFINER = CURRENT_USER TRIGGER   extensionui2.country_group_AFTER_DELETE 
AFTER DELETE ON country_group 
FOR EACH ROW
BEGIN
    DECLARE w FLOAT(5,2);
    DECLARE c INT;
    DECLARE s FLOAT(5,2);

    SET w = OLD.weight;
    SELECT count(*) into c FROM country_group WHERE code = OLD.code;

    SET s = w / c;
    UPDATE country_group SET weight = weight + s WHERE code = OLD.code;
END;

但是我得到这个错误：

Operation failed: There was an error while applying the SQL script to the database.
Executing:
DELETE FROM `extensionui2`.`country_group` WHERE `code`='ms' and`group_id`='9';

ERROR 1442: 1442: Can't update table 'country_group' in stored  function/trigger because it is already used by statement which invoked this stored function/trigger.
SQL Statement:
DELETE FROM `extensionui2`.`country_group` WHERE `code`='ms' and`group_id`='9'

我需要更改触发代码中的哪些内容才能使其正常工作？

Answer 1

MySQL 错误 1442 是由于 MySQL 中的限制。不允许触发器更新定义触发器的 table 中的任何行。

A stored function or trigger cannot modify a table that is already being used (for reading or writing) by the statement that invoked the function or trigger.

因此，不可能在触发器的上下文中执行您想执行的操作。

如何在删除触发器后更新 table 中的行

How to update rows in table in after delete trigger

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