题目内容
在Visual FoxPro中，数据库表中不允许有重复记录是通过指定______来实现的。
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TextOne of the advantages of taking notes is that it forces you to pay closer attention to the class lecture. If you listen (26) to a professor who is talking on and on for an hour or so, your mind will often (27) and your attention lessen. You arc sitting in class and listening, but that (28) you are doing; (29) when you listen actively you have to pay more careful and (30) attention to what (31) . This is because you are trying to (32) what you bear into an (33) , shortened written form. As a foreign student, you may find (34) very difficult to listen and write notes (35) at the same time. It is difficult (36) , but you will learn how to do (37) with practice. You (38) afraid you will forget what you are listening to (39) you are listening and writing at same time, but the studies of researchers (40) the value of note-taking in (41) lecture material have shown that learners remember (42) reproduced in some note form much better than lecture information they have listened to (43) down in note form. So doing two things at the same time is better than doing one thing. (44) . We do not say it is (45) ; we say it is better. 28().
TextOne of the advantages of taking notes is that it forces you to pay closer attention to the class lecture. If you listen (26) to a professor who is talking on and on for an hour or so, your mind will often (27) and your attention lessen. You arc sitting in class and listening, but that (28) you are doing; (29) when you listen actively you have to pay more careful and (30) attention to what (31) . This is because you are trying to (32) what you bear into an (33) , shortened written form. As a foreign student, you may find (34) very difficult to listen and write notes (35) at the same time. It is difficult (36) , but you will learn how to do (37) with practice. You (38) afraid you will forget what you are listening to (39) you are listening and writing at same time, but the studies of researchers (40) the value of note-taking in (41) lecture material have shown that learners remember (42) reproduced in some note form much better than lecture information they have listened to (43) down in note form. So doing two things at the same time is better than doing one thing. (44) . We do not say it is (45) ; we say it is better. 30().
使用如下三个数据库表： 学生(学号C(8)，姓名C(8)，性别C(2)，班级C(8)) 课程(课程编号C(8)，课程名称C(20)) 成绩(学号C(8)，课程编号C(8)，成绩N(5，1)) 检索还未确定成绩的学生选课信息，正确的SQL命令是
使用如下三个数据库表： 学生(学号C(8)，姓名C(8)，性别C(2)，班级C(8)) 课程(课程编号C(8)，课程名称C(20)) 成绩(学号C(8)，课程编号C(8)，成绩N(5，1)) 查询所有选修了“高等数学”的学生的“高等数学”成绩，要求得到的信息包括学生姓名和成绩，并按成绩由低到高的顺序排列，下列语句正确的是
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