即使我有"删除级联",获取"外键约束失败"

Question

我认为ON DELETE CASCADE的意思是这不会发生.:\我有以下表格:

CREATE TABLE Tweets (
    tweetID INTEGER                 NOT NULL AUTO_INCREMENT,
    userID INTEGER                  NOT NULL,
    content VARCHAR(140)            NOT NULL,
    dateTime TIMESTAMP              NOT NULL DEFAULT CURRENT_TIMESTAMP,
    hasPoll INTEGER                 NOT NULL,
    visible INTEGER                 NOT NULL DEFAULT 1,
    PRIMARY KEY (tweetID),
    FOREIGN KEY (userID) REFERENCES Users(userID)
    ON DELETE CASCADE
);

CREATE TABLE Polls (
    pollID INTEGER NOT NULL AUTO_INCREMENT,
    tweetID INTEGER NOT NULL,
    pollOptionText VARCHAR(300),
    PRIMARY KEY (pollID),
    FOREIGN KEY (tweetID) REFERENCES Tweets(tweetID)
);

问题是,当我尝试删除附加了Poll的推文时,我收到以下错误(通过Flask):

_mysql_exceptions.IntegrityError
IntegrityError: (1451, 'Cannot delete or update a parent row: a foreign key constraint fails (`twitter`.`polls`, CONSTRAINT `polls_ibfk_1` FOREIGN KEY (`tweetID`) REFERENCES `Tweets` (`tweetID`))')

请帮忙!

Answer 1

这确实是重点on delete cascade.您收到错误,因为您的代码未on delete cascade从"poll" 声明为"tweet".

CREATE TABLE Polls (
    pollID INTEGER NOT NULL AUTO_INCREMENT,
    tweetID INTEGER NOT NULL,
    pollOptionText VARCHAR(300),
    PRIMARY KEY (pollID),
    FOREIGN KEY (tweetID) REFERENCES Tweets(tweetID)
      ON DELETE CASCADE
);

当在"推文"中删除相应的行时,这将删除"民意调查"中的行.