MySQL：触发器将根据 DELETE 和 INSERT 增加列值

Question

我想设置一个触发器来增加列值。如果我执行 INSERT，我希望它为 + 1，如果我执行 DELETE，我希望它为 -1。

INSERT INTO `users saved` SET `userid` = '$user->id', `topicid` = '$topicid'
DELETE FROM `users saved` WHERE `userid` = '$user->id' AND `topicid` = '$topicid' LIMIT 1

数据库架构

`users saved`
id | userid | topicid

`total`
topicid | value

我希望触发器生效的table是total，我希望值列（int）上升或下降。

我不确定从哪里开始。

Answer 1

虽然我没有测试，但应该可以，删除语句非常相似：

CREATE TRIGGER increment_value_on_insert 
    AFTER INSERT ON `users saved`
    REFERENCING
        NEW ROW as new_row
    FOR EACH ROW BEGIN
    UPDATE total
    SET value = value+1
    WHERE
     topicid = new_row.topicid
    END

MySQL：触发器将根据 DELETE 和 INSERT 增加列值

MySQL: Trigger that'll increment a columns value, based on DELETE and INSERT

mysql

sql

triggers

insert

sql-delete