【题解】Quiz: Many-to-Many Relationships and Python (Using Databases with Python)

吐槽：有点难...= =听了课还是差点没满分...

题目：

1. In the following Python code sequence (assuming cur is a SQLite cursor object),

cur.execute('SELECT count FROM Counts WHERE org = ? ', (org, ))

row = cur.fetchone()

what is the value in row if no rows match the WHERE clause?

A. An empty list

B. None

C. -1

D. An empty dictionary

fetchone() ：返回单个的元组，也就是一条记录(row)，如果没有结果，则返回None（https://blog.csdn.net/Odaokai/article/details/101026437）。

2. What does the LIMIT clause in the following SQL accomplish?

SELECT org, count FROM Counts

ORDER BY count DESC LIMIT 10

A. It only retrieves the first 10 rows from the table

B. It only sorts on the first 10 characters of the column

C. It reverses the sort order if there are more than 10 rows

D. It avoids reading data from any table other than Counts

limit限制了检索条数（https://www.runoob.com/sqlite/sqlite-limit-clause.html）。

3. What does the executescript() method in the Python SQLite cursor object do that the normal execute() method does not do?

A. It allows embeded Python to be executed

B. It allows multiple SQL statements separated by semicolons

C. It allows database tables to be created

D. It allows embedded JavaScript to be executed

excutescript() 是一次可以执行多条sql（https://zhidao.baidu.com/question/491140202514932212.html）。

4. (多选) What do we generally avoid in a many-to-many junction table?

A. An AUTOINCREMENT primary key column

B. A logical key

C. Two foreign keys

D. Data items specific to the many-to-many relationship

juction table有user_id, course_id, role, PRIMARY KEY(user_id, course_id)，详情见讲座第一节。