Database postgraduate retest questions (East China Science and Technology)

Description: Collect the short answer questions of the calculation network and the database in the purchased Huali re-examination data, for preparation for the test.
This has a detailed
database system and principle design (third edition). Summary of knowledge points in the book (1)
Database system and principle Design (Third Edition) Summary of Knowledge Points of the Book (2)
Database System and Principle Design (Third Edition) Summary of Knowledge Points of the Book (3) Knowledge Points of the
Seventh Edition "Computer Network" Knowledge Points + Kingway Exercises (Physical Layer + Link Layer)
The seventh edition of "Computer Network" knowledge points + kingly exercises (network layer + transmission layer
computer network postgraduate examination questions (East China Science and Technology)

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• Compared with the non-relational model, the disadvantage of the relational model is: the access path is transparent to the user, and query optimization is required
• ER diagram is a conceptual model
• Convert the ER model into a relational model, which belongs to the logical design of the database
• SQL language has functions: data definition, data manipulation, data control (data query)
• The code of a relationship contains all attributes, and it reaches at least the first-level normal form: 3NF
• The three elements of the data model are: data structure, data operation and data integrity constraints
• The relationship between DB DBMS and DBS is: DBS includes DB and DBMS
• Description of the physical storage method of the database : internal mode
• What describes the global logical structure and characteristics of all data in the database is: mode
• In the three-level database mode, the number of modes: only one
• SQL language supports the external mode, mode and internal mode structure of the database. The outer mode corresponds to the view and part of the basic table , the mode corresponds to the **(whole) basic table**, and the inner mode corresponds to the storage file
• The main function of introducing the secondary image in the three-level database model is to improve the independence of data and programs
• How to construct a suitable data logical structure is the main problem that the relational database standardization theory solves.
• Access method design is the task of the physical structure design phase of database design
• In a relational database, when the type of relationship changes, the user program can also remain unchanged. This is the logical independence of the data
• In the three-level mode architecture, the mapping between the mode and the inner mode realizes the physical independence of the data
• To ensure data independence between databases , it is necessary to modify the two mappings between the three-layer mode
• The independence of physical data in a database system refers to: the physical mode of the application and the database stored on the disk is independent
• Shared locks are compatible with shared locks, no other combinations will work. A data object Q can have multiple shared locks S (owned by different transactions) at the same time , but there can only be one exclusive lock X at any time .
• The logical independence of the database is provided by the external schema/schema mapping
• Relational operation : select\project\connect\divide
• Selection, projection (Π), set union, set difference, and Cartesian product are five basic relational operations .
• From the perspective of relationship standardization theory, there may be four problems in a relationship that only meets 1NF: data redundancy, large insertion exception, modification exception and deletion exception
• The main method of concurrency control is the blocking mechanism
• FIG ER conflict between the main attribute naming conflict Conflict Conflicts three kinds
• There are three stages in the development of database management technology: manual management stage\file system stage\database stage.
  There is no special software to manage the data in the manual management stage.
• In principle, a SQL statement can generate or process a set of records, while the programming language can only process one record at a time. For this reason, two processing methods must be coordinated. This is solved by using the cursor mechanism.
• In a relationship, any attribute contained in the candidate code becomes the primary attribute
• The abnormal delete operation in the normalization of the relationship refers to: the data that should not be deleted is deleted
• The main elements of the ER diagram are: entity type attribute connection
• The code of the relational mode R is single attribute , then R must be the second normal form
• If all the attributes in the relational pattern R are primary attributes , the degree of normalization of R reaches at least the third normal form. Regarding the normal form, this has a detailed definition.
• Database systems generally include: database database management system application system database administrators and users
• The general steps of database design: demand analysis, conceptual structure design, logical structure design, physical structure design, database implementation, operation and maintenance, etc.
• The characteristics of the database are: data sharing, data independence, reducing data redundancy, avoiding data inconsistencies and strengthening data protection
• Information requirements indicate the data and structure required by an organization.
  Processing requirements indicate the data processing that an organization needs frequently.
• The three inference rules of the Armstrong axiom system are the transfer rate of the augmentation rate of the reflexive law

Explain the difference and connection between views and basic tables

View is derived from a base table or several tables, he different from the basic table, which is a virtual table .
Database stored only defined in the view , without attempting to store data corresponding to the data on the original base table In, when the data in the basic table changes, the data queried from the view also changes . Once a
view is defined, it can be queried and deleted like a basic table, or a new view can be defined on top of a view, but right There are restrictions on view update operations.

Transaction characteristics, namely ACID

• Atomicity: All operations included in the transaction are either done or not done
• Consistency: The transaction must change the database from one consistent state to another consistent state
• Isolation: The operations and data used within a transaction are isolated from concurrent transactions
• Persistence: Once the transaction is committed, the changes to the database are permanent

Referential integrity rules of the relational model

If the attribute (or attribute group) F is the outer code of the basic relationship R, it corresponds to the main code Ks of the basic relationship S (the basic relationship RS is not necessarily a different relationship,
then for each tuple in R on F value must be: take a null value (F value of each attribute are null), or equal to the primary key value of a tuple in S .

Briefly describe the database recovery strategy when the system fails

Day forward scanning log files to find fault occurs before the transaction has been submitted to the transaction ID included in the REDO queue while to find out when a fault occurs has not yet completed the transaction, which marks the transaction into NUDO queue. Queue for UNDO Each thing in the REDO queue is undone , and each thing in the REDO queue is redone .