slq语句 substring (firstname, 1, 3)+ substring (lastname, 1, 2...答:第一种情况如果firstname是字符串的话,那么 substring (firstname, 1, 3)返回的结果是ir substring (lastname, 1, 2)返回的结果是a substring (firstname, 1, 3)+ substring (lastname, 1, 2)就是返回字符串ira 第二种情况,如果firstname,lastname代表列的值的话,那下面肯定有where子句那...