Question

我正在尝试创建一个包含2个事件的表bus。一个AutoDelete用于维护总线表中的数据（这个工作），另一个用于删除表中没有记录的表。 AutoDelete我不知道如何在事件SELECT COUNT(*) FROM bus中将条件设置为DropBusTable以使其生效，因为我没有时间作为另一个我有条件的时间。

我感谢任何帮助。

   stt.execute("CREATE TABLE IF NOT EXISTS bus"
            + "(id INT(11) NOT NULL AUTO_INCREMENT PRIMARY KEY,"
            + "mac VARCHAR(30) NOT NULL UNIQUE,"
            + "route int(11) NOT NULL,"
            + "latitude FLOAT(10,6) NOT NULL,"
            + "longitude FLOAT(10,6) NOT NULL,"
            + "created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP)");

    stt.execute("CREATE EVENT IF NOT EXISTS  AutoDelete "
            + "ON SCHEDULE EVERY 3 MINUTE "
            + "DO "
            + "DELETE FROM bus WHERE created_at < (NOW() - INTERVAL 3 MINUTE)");

    // I tried this statement here but it does not work.
    stt.execute("CREATE EVENT IF NOT EXISTS  DropBusTable "
            + "Do "
            + "DROP TABLE IF EXISTS  bus");

Answer 1

您可以使用以下方法重置计数器：

ALTER TABLE <table_name> AUTO_INCREMENT = 1

将其添加到现有任务中：

  stt.execute("CREATE EVENT IF NOT EXISTS  AutoDelete "
            + "ON SCHEDULE EVERY 3 MINUTE "
            + "DO BEGIN"
            + "DELETE FROM bus WHERE created_at < (NOW() - INTERVAL 3  MINUTE);"
            + "ALTER TABLE bus AUTO_INCREMENT = 1 ;"
            + "END;");

有关详情，请参阅 article 。

如果不存在记录，则将事件设置为删除表

1 个答案: