假定 user 表中有一个 username 字段 , 下面选项,可以给 username 字段添加一个 un 别名的 SQL 语句是 A. select username is un from user; B. select username as un from user; C. select username, un from user; D. select username un from user;
【单选题】If the quantity of good A (QA) is plotted along the horizontal axis, the quantity of good B (QB) is plotted along the vertical axis, the price of good A is PA, the price of good B is PB and the consum...