Quiz#

本节为sjl老师数据库课后随堂习题的汇总

week1#

The feature of database;
The duty of database administrator;

week2#

关系代数的基本操作有什么
不同操作之后的元祖数量

week3#

sql语句考察，考点完全同22.2考题
考察select p1.id from person P1, person P2 where p1.gender = p2.gender group by p1.id having count(*) > 1;的结果即统计相同性别且人数大于二的性别的人数。

由于P1和P2是同一个表做product，因此结果的数量可能大于表中行数。

week6#

把ER图转化成关系模式的时候，entity中的多值属性必须单独转换成一个关系模式。
把ER图转化成关系模式的时候，Many-to-Many的关系必须转换成一个关系模式。
把weak entity set转换成关系模式时，构成关系模式主键的属性是：

The union of the discriminator of the weak entity set and the primary key of the identifying strong entity set.

week7#

\(F={AB \to C, C \to D}\), set F hold on the relation R(ABCDE). 1. which functional dependency is in the closure of F? > \(AB \to D\), \(AB \to CD\). 2. The closure of the attribute set {AC} is: > {ACD} 3. What is the candidate key of R? > {ABE} 4. Which decomposition is lossless join? > - \(R_1(A, B, C, E)\), \(R_2(C, D)\) [Y] > - \(R_1(A, B, C, E)\), \(R_2(A, B, D)\) [Y] > - \(R_1(A, B, D, E)\), \(R_2(A, B, C)\) [Y] > - \(R_1(A, B, C)\), \(R_2(C, D, E)\) [N]

考察Canonical Cover;
考察BCNF;

week9#

which physical storage media is non-volatile? > flash memory | magnetic disk | SSD | magnetic tape | optical disk
which physical storage medias belong to secondary storage? > flash memory | magnetic disk | SSD
which term represents the time that the disk controller takes to reposition the disk arm over the correct track?(考察Performance Measures of Disks) > seek time
What is the right approach to optimizing data access on a disk? > - Buffering > - Read-ahead > - defragment the file system > - Non-volatile write buffer > - Log disk

⅚. What's MTTF & IOPS? > - MTTF: Mean Time To Failure > - IOPS: Input/Output Operations Per Second

What is contained in the header of slotted page?
Judge different file organization!!!
Which statement is incorrect? (D) > - A. For heap file organization, records can be placed anywhere in the file where there is space > - B. Database system seeks to minimize the num of block transfers between the disk and memory > - C. If the needed block is not in the buffer, the buffer manager will replace some block in the buffer. > - D. LRUs are the most efficient replacement policy
LRU Quiz

week10#

Indexing mechanisms are used to speed up access to desired data. [Y]
Range query returns records with an attribute value falling in a specified range of values. [Y]
Secondary index is an index whose search key specifies an order same as the sequential order of the file. [N]
In an dense index, index records for every search-key value appear in the index file. [Y]
B+ tree path length is same as the height of the tree. [Y]
If the root of a b plus tree is a leaf node, the tree has at least two children. [Y]
In databases, a node of a b plus tree is generally the same size as a disk block. [Y]
The leaf nodes of a b plus tree file organization store records, instead of pointers to records. [Y]
Bitmap indices are useful for queries on multiple attributes, not particularly useful for single attribute queries. [Y]

Benefits of LSM approach: (a,b,c) (a) Inserts are done using only sequential I/O operations. (b) Leave nodes are full, avoid space waste. © Reduced number of I/O operations per record inserted as compared to B+ tree. (d) Queris have to search multiple trees. (e) Entire content of each level copied multiple times.