Question

我一直在尝试根据数据插入表格中的表格中设置自动增量，

因为这被标记为重复，我已经查看了其他问题，我认为我的主要问题是误解了触发器的语法，特别是行：

WHERE ID = NEW.ID;

MySQL Block：

CREATE TABLE Members(
    ID  INT  UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
    FIRST_NAME  TEXT(16),
    LAST_NAME  TEXT(16),
    TITLE  TEXT(7), /** 7 CHARS for  'Student'*/
    INSTITUTION  VARCHAR(2048),
    No_Publications INT NOT NULL,
    PRIMARY KEY(ID)
  );
CREATE TABLE Papers(
    ISBN  INT UNSIGNED NOT NULL UNIQUE,
    Title  TEXT(4),
    Publish_Date  DATE NOT NULL,
    Topic  TEXT(128),
    PRIMARY KEY(ISBN)
  );
  CREATE TABLE Publications(
    Researcher_ID  INT  UNSIGNED NOT NULL UNIQUE,
    ISBN  INT UNSIGNED NOT NULL UNIQUE,
    PRIMARY KEY (Researcher_ID, ISBN),
    FOREIGN KEY(Researcher_ID) REFERENCES Members(ID) ON DELETE RESTRICT ON UPDATE CASCADE,
    FOREIGN KEY(ISBN) REFERENCES Papers(ISBN) ON DELETE RESTRICT ON UPDATE CASCADE /**Used in
    many to many relations*/
  );

  CREATE TRIGGER New_Publication AFTER INSERT ON Publications
  FOR EACH ROW
  BEGIN
  UPDATE Members SET No_Publications = No_Publications + 1 WHERE ID = NEW.ID;
  END;

编辑：插入Publications表后，我希望Members表中的No_Publication列增加一个

Answer 1

id表格中没有publications字段，因此不能有任何NEW.ID。你必须在mysql中收到一个未知的字段错误。 publications的create table语句包含有关在更新中使用哪个字段的线索：

FOREIGN KEY(Researcher_ID) REFERENCES Members(ID)

因此，更新应如下所示：

UPDATE Members SET No_Publications = No_Publications + 1 WHERE ID = NEW.Researcher_ID

此外，不需要begin ... end，因为触发器主体包含一个sql语句：

CREATE TRIGGER New_Publication AFTER INSERT ON Publications
  FOR EACH ROW
  UPDATE Members SET No_Publications = No_Publications + 1 WHERE ID = NEW.Researcher_ID;

自动使用MySQL触发器增加值

1 个答案: