The procedure of the test interview (Database concept knowledge) and the test interview

The procedure of the test interview (Database concept knowledge) and the test interview

Section 1:

Related Concepts:

1> Data: Data is the basic object stored in the database and a symbolic record describing a transaction.

2> DataBase: a DataBase is a collection of large amounts of data that has been stored in a computer for a long time and can be shared.

3-> DBMS: a database management system, which is a layer of data management software between users and operating systems. It is used to scientifically organize, store, and manage data and efficiently obtain and maintain data.

4-> DBS: database system refers to the system after the database is introduced into the computer system. Generally, it is composed of a database, a database management system, and a database administrator.

5-> Data Model: it is a tool used to abstract, represent, and process real-world data and information. It is a simulation of the real-world. The core and foundation of a Database. Its components include data structures, data operations, and integrity constraints.

6-> conceptual model: it is also called an information model. It is used to model data and information based on the user's point of view and is mainly used for database design.

7-> logical model: data is modeled based on the computer system and used for DBMS implementation.

8-> physical model: abstraction of the lowest data layer. It describes the representation and access methods of data in the system, and the storage or access methods on tapes or disks, is for computer systems

9-> entity and attribute: a transaction that exists objectively and can be differentiated from each other is called an entity. Some features of an object are called attributes.

10-> E-R diagram: entity-relational diagram, used to describe real world transactions and their relations, is the main tool of the concept design of database

11-> Relationship Mode: from the user's point of view, the relationship mode is composed of a series of relationships. The data structure of each link is a standardized two-dimensional table.

12-> type/value: Type describes the structure and attributes of a type of data. A value is a specific value assignment of the type, and it is a type instance.

13-> database mode: it refers to the logical structure (name, type, value range, etc.) of all data in the database and the relationship between features (data, and data-related security and integrity requirements)

14-> three-level system structure of the database: external mode, mode, and internal mode

15-> the internal mode of the database, also known as the storage mode, describes the physical structure and storage mode of the database. It is the internal representation of data in the database. A database has only one internal mode.

16-> external database mode: Also known as the sub-mode or user mode. It is the feature description of the local data and logical structure that the database user can see and use. It is a view of the database user.

17-> database secondary image: external mode/mode image, mode/internal mode image

Key knowledge:

1-> A database system consists of a database, a database management system, an application, and a database administrator.

2-> the components of the data model are: data structure, data operations, and integrity constraints

3-> there are three types of real-world relationships: one-to-one, one-to-many, and multiple-to-many.

4-> common data models include: relationship, hierarchy, mesh object orientation, object relationship ing, etc.

5-> integrity constraints of a relational model include entity integrity, referential integrity, and user-defined integrity.

6-> describe the meaning and function of the database level-3 mode and level-2 Image

The three-level database mode reflects three different levels of data abstraction: the mode describes the logical structure and features of all data in the database. The internal mode, also known as the storage mode, describes the physical structure and storage mode of the database. The external mode, also known as the submode or user mode, describes the logical structure and features of local data related to specific database users.

The database level-3 mode implements the connection and conversion between the three abstract layers in the DBMS through the second-level image. The external mode is oriented to applications. The external mode/mode image is connected with the logical mode to realize the logical independence of data. Mode/internal mode images establish one-to-one ing between the mode and internal mode to achieve physical independence of data.

 

Section 2:

Related Concepts

1-> primary key: a key or candidate key that uniquely identifies a tuples or a link. If a link has multiple candidate keys, select one of them as the primary key.

2-> foreign key: if one or more attributes of a link reference the primary key of another link, this or this group of attributes is called an external code.

3-> Relational Database: a database created based on a relational model is called a relational database. It is a collection of all the relationships in an application field.

4-> relational model: in short, relational model is a definition of relational, including link attribute composition, data type of each attribute, dependency between attributes, tuples semantics and integrity constraints, etc.

5-> Object Integrity: The primary key cannot be blank and the values are not repeated.

6-> integrity of reference: used to maintain reference relationships between entities. It requires that the foreign key of a link be either null or take the primary key value corresponding to the referenced Link

7-> User-Defined integrity: the application data must meet the semantic constraints.

Key knowledge

1-> relational database languages are classified into relational algebra, relational calculus, and structured query languages.

2-> five basic operations of a link are selection, projection, sum, difference, and Cartesian product.

3-> description of the link mode, which is expressed in the form of 5 tuples: R (U, D, DOM, F)

Here, R ----- Link name U ----- is a set of attribute names of the link.

D ----- the domain DOM of the attribute group U ----- the image set of the attribute to the domain F ----- indicates the dependency between attributes

 

Section 3:

Related Concepts:

1-> SQL: Abbreviation of structured query language, which is the standard language of relational databases. SQL is a common and extremely functional relational database language. It is a standard interface for relational inventory and serves as the basis for mutual operations between different databases. Integrates dataset query, data operations, data definition, and data control functions.

2-> data definition: The data definition function includes schema definition, table definition, and view index definition.

3-> nested query: place a query block in the WHERE or HAVING directory of another query block.

Key knowledge:

1-> the operation objects of SQL data definition statements include schema, table, view, and index.

2-> the command verbs of SQL data definition statements are CREATE, DROP, and ALTER.

3-> DBMS indexes are generally implemented using B + trees or HASH.

4-> indexes can be divided into three categories: unique index, non-unique index, and clustered index.

5-> the SQL statement used to create a table is in the following format:

Create table <TABLE Name> (

<Column Name> <data type> [<column-level integrity constraints>]

);

The <data type> can be a variety of data types supported by the database system, including length and accuracy.

Column-level integrity constraints are integrity constraints for a single column, including PRIMARYKEY (column Name List) unique not null.

Table-level integrity constraints can be based on the constraints of multiple columns in the table, including the primary key (column name list) and foreign key references table name (column name)

6-> general format of SQL index creation statements

CREATE [UNIQUE] [CLUSTER] INDEX <INDEX Name>

ON <Table Name> (<column Name List>)

UNIQUE: Indicates creating a UNIQUE index. The default value is non-UNIQUE index.

CLUSTER: Creates a clustered index. The default value is non-clustered index.

7-> the general format of SQL query statements is

SELECT [ALL | DISTINCT] <arithmetic expression list> FROM <Table name or view Name List>

[WHERE <condition expression 1>]

[Group by <Attribute Table 1>] [HAVIN <conditional expression 2>]

[Order by <Attribute Table 2>] [ASC | DESC]

 

Section 4

Concepts and knowledge

1-> A trigger is a special event-driven process defined on a basic table. Automatically activated by the server, which can perform more complex checks and operations, and has more precise and powerful data control capabilities. Use the create trigger command to CREATE a TRIGGER

2-> there are three security problems in computer systems: technical security, management security, and policy and law.

3-> TCSEC and TDI standards consist of security policies, responsibilities, guarantees, and documents.

4-> common access control methods include autonomous access control and forced access control.

5-> autonomous access control includes GRANT and REVOKE.

The following are common autonomous control commands:

Grant all permissions to Student and Crouse tables to all users

Grant all priviliges on table Student, Course to public;

Grant the query permission and name modification permission to Student table U4

Grant select, UPDATE (Sname) on table Student TO U4;

Grant the insert permission to the SC table to the U5 user and allow the user to spread the permission.

Grant insert on table SC TO U5 WHIT GRANT OPTION;

Detaches the INSERT permission of user U5 on the SC table and revokes the permission that is propagated by the user.

Revoke insert on table SC FROM U5 CASCADE

Create a role R1 with the data query and update permissions on the Student table.

Create role R1;

Geant select, update on table Student TO R1;

Audit Operations on modifying the Student table structure

Audit alter on Student;

 

Public Institution examination, written examination subjects for computer, network, database and other professional knowledge, whether there are people, what type and scope of PEN questions, who should

Let's see how it adds popularity and hope you can find a satisfactory answer!

How do you understand the concept of database transactions? Simple Description

Database transactions are a series of operations performed as a single logical unit of work.
Imagine a transaction for online shopping. the payment process includes at least the following database operations:
· Update the inventory information of the products purchased by the customer
· Save customer payment information-may include interaction with the banking system
· Generate an order and save it to the database
· Update user information, such as the number of shopping items
Under normal circumstances, these operations will go smoothly, the transaction will be successful, and all database information related to the transaction will be updated. However, if an error occurs in any part of the process, for example, an exception occurs when updating the inventory information, or the customer's bank account has insufficient deposits, the transaction will fail. Once a transaction fails, all the information in the database must remain unchanged before the transaction. For example, if the last step fails to update the user information, the transaction fails, make sure that the failed transaction does not affect the database status-the inventory information is not updated, the user has not paid, and the order has not been generated. Otherwise, the database information will be messy and unpredictable.
Database transactions are a technology used to ensure the stability and predictability of transactions in such circumstances.
[Edit this section] ACID attributes of database transactions
Transaction Processing ensures that data-oriented resources are not updated permanently unless all operations in the transaction unit are successfully completed. By combining a set of related operations into a unit that either succeeds or fails, you can simplify error recovery and make the application more reliable. To become a transaction, a logical unit of work must meet the so-called ACID (atomicity, consistency, isolation, and durability) attributes:
· Atomicity (atomic)
A transaction must be an atomic unit of work. modifications to its data must either be performed in all or not. Generally, operations associated with a transaction share a common goal and are mutually dependent. If the system executes only one subset of these operations, the overall goal of the transaction may be broken. Atomicity eliminates the possibility of a subset of system processing operations.
· Consistent)
When the transaction is completed, all data must be consistent. In related databases, all rules must be applied to transaction modifications to maintain the integrity of all data. At the end of the transaction, all internal data structures (such as B-tree indexes or two-way linked lists) must be correct. Some maintenance consistency responsibilities are borne by application developers who must ensure that the application has enforced all known integrity constraints. For example, when developing an application for transfer, do not move any decimal point during transfer.
· Isolation (insulation)
Modifications made by a concurrent firm must be isolated from those made by any other concurrent firm. The status of the data when the transaction is viewing the data is either the status before the transaction is modified or the status after the transaction is modified. The transaction does not view the data in the intermediate status. This is called serializability because it can reload the starting data and replays a series of transactions so that the State at the end of the data is the same as that of the original transaction execution. When a transaction is serializable, the highest isolation level is obtained. At this level, the results obtained from a group of parallel transactions are the same as those obtained by running each firm consecutively. Since high isolation limits the number of transactions that can be executed in parallel, some applications reduce the isolation level in exchange for greater throughput.
· Duration)
After the transaction is completed, its impact on the system is permanent. This modification will remain even if a fatal system failure occurs.
[Edit this section] DBMS responsibility
All enterprise-level database management systems (DBMS) have the responsibility to provide a mechanism to ensure the physical integrity of transactions. For the commonly used SQL Server2000 system, it has mechanisms such as locking device isolation transactions and recording devices to ensure transaction persistence. Therefore, we do not have to worry about the physical integrity of database transactions, but should focus on the use of database transactions, the impact of transactions on performance, and how to use transactions.
This document describes how to use C # To manipulate database transactions in the. net Framework.
Experience the transaction mechanism of SQL language
As a large enterprise-level database, SQL Server2000 provides excellent support for transactions... the remaining full text>