MySQL 不接受循环结束指令

Question

我正在尝试在插入事件之后创建触发器；这是触发器的定义：

 BEGIN
    DECLARE stud INT(11) DEFAULT 0;
    DECLARE cd INT(11) DEFAULT 0;
    DECLARE sw CURSOR FOR 
        (SELECT CodiceStudente FROM Listastudenticorsi WHERE CodiceCorso IN
            (SELECT CodiceCorso FROM Listanews WHERE CodiceNews IN
                (SELECT MAX(Codice) FROM News)));
    DECLARE cod CURSOR FOR
        (SELECT CodiceDocente FROM Listanews WHERE CodiceNews IN
               (SELECT MAX(Codice) FROM News));
    OPEN sw;
    OPEN cod;
    get_loop: LOOP
    FETCH sw INTO stud;
    FETCH cod INTO cd;
    INSERT INTO Inbox(Mittente, Destinatario, Oggetto, Contenuto, Data) VALUES (cd, stud, "Nuova news", "", CURDATE());
    END LOOP get_loop;
END

由于某些原因，MySQL 不允许我创建它：它说我必须在第 17 行检查“LOOP;END”附近的语法，但据我所知，那里的语法是正确的......我不明白出了什么问题，即使我将循环名称放在结束循环之后，也会出现错误。

我不确定错误是否可能在 INSERT 指令中：我不确定变量 @cod 的使用；它始终是一个独特的价值，但我不确定是否是导致问题的原因。如果是这样，我该如何更改该指令以获得相同的结果？

Answer 1

您缺少第 17 行的 END IF; 语句

BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE stud VARCHAR(255) DEFAULT "";
    DECLARE sw CURSOR FOR 
        (SELECT CodiceStudente FROM Listastudenticorsi WHERE CodiceCorso IN
            (SELECT CodiceCorso FROM Listanews WHERE CodiceNews IN
                (SELECT MAX(Codice) FROM News)));

    SET @cod = (SELECT CodiceDocente FROM Listanews WHERE CodiceNews IN
               (SELECT MAX(Codice) FROM News));
    OPEN sw;
    get_loop: LOOP
    FETCH sw INTO stud;
        IF done THEN
        LEAVE get_loop;
        END IF;
    INSERT INTO Inbox(Mittente, Destinatario, Oggetto, Contenuto, Data) VALUES (@cod, @i, stud, "", CURDATE());
    END LOOP get_loop;
END;

Answer 2

我不确定您为什么会收到该错误，但您根本不需要loop。只需执行以下操作：

INSERT INTO Inbox(Mittente, Destinatario, Oggetto, Contenuto, Data)
    SELECT @cod, CodiceStudente, 'Nuova news', '', CURDATE()
    FROM Listastudenticorsi
    WHERE CodiceCorso IN (SELECT CodiceCorso 
                          FROM Listanews
                          WHERE CodiceNews IN (SELECT MAX(Codice) FROM News));