条件触发器的Django迁移sql

我想创建一个触发器，仅在满足条件时插入表。 我尝试过使用 IF/BEGIN/END 和 WHERE 的各种组合，但 Django 每次都会返回 SQL 语法错误。

这里，type_user_id指的是触发该事件的人，user_id指的是接收到通知的人。仅当他们不是同一个人时才会触发。

operations = [

    migrations.RunSQL(
        "DROP TRIGGER like_notification",
        """
        CREATE TRIGGER like_notification AFTER INSERT ON user_likes_article
        FOR EACH ROW
        IF (select user_id from channel WHERE channel_id IN
            (SELECT channel_id FROM article WHERE article_id = NEW.article_id)) <> NEW.user_id
        BEGIN
            INSERT INTO notification (type, type_id, article_id, is_read, type_user_id, user_id)
                VALUES ('like', NEW.article_id, NEW.article_id, false, NEW.user_id,
                    (SELECT user_id from channel WHERE channel_id IN
                        (SELECT channel_id FROM article WHERE article_id = NEW.article_id)
                    )
                )
        END;
        """
    )
]

>>>django.db.utils.ProgrammingError: (1064, "You have an error in your SQL syntax; 
check the manual that corresponds to your MariaDB server version for the right syntax 
to use near 'BEGIN\n INSERT INTO notification (type, type_id, article_id, is_re' at line 5")

and

CREATE TRIGGER like_notification AFTER INSERT ON user_likes_article
        FOR EACH ROW
        BEGIN
            DECLARE @user_same Boolean;
            SELECT 1 into @user_same
            FROM channel
            WHERE channel_id IN (select channel_id FROM article where article_id = NEW.article_id)
            AND user_id = NEW.user_id;

            IF @user_same <> 1
            THEN
                INSERT INTO notification (type, type_id, article_id, is_read, type_user_id, user_id,)
                VALUES ('like', NEW.article_id, NEW.article_id, false, NEW.user_id, (
                    SELECT user_id from channel WHERE channel_id IN (
                         SELECT channel_id FROM article WHERE article_id = NEW.article_id)
                    )
            END IF;
        END;

>>>You have an error in your SQL syntax; check the manual that corresponds to your 
MariaDB server version for the right syntax to use near '@user_same Boolean;\n                SELECT 1 into @user_same\n                FRO' at line 4"

and

CREATE TRIGGER like_notification AFTER INSERT ON user_likes_article
        FOR EACH ROW
        INSERT INTO notification (type, type_id, article_id, is_read, type_user_iduser_id)
        VALUES ('like', NEW.article_id, NEW.article_id, false, NEW.user_id,
            (
            SELECT user_id from channel WHERE channel_id IN
                (SELECT channel_id FROM article WHERE article_id = NEW.article_id)
            )
        WHERE NOT user_id = NEW.user_id;

>>>You have an error in your SQL syntax; check the manual that corresponds to your 
MariaDB server version for the right syntax to use near 'WHERE NOT user

我真的不明白为什么它们都不起作用。任何帮助将非常感激！

@variables不是DECLARED.

Either:

DECLARE user_same BOOLEAN;
SELECT 1 INTO user_same WHERE ...

or

SELECT @user_same := 1 WHERE ...

更好的是，这避免了对变量的需要。

IF (EXISTS SELECT * FROM ...)

另外，不要使用构造IN ( SELECT ... );通常最好使用WHERE EXISTS ( SELECT * FROM ... ) or JOIN ... ON ....

（修复这些问题后可能还会出现更多问题。）