The brief questions of previous years do not apply to this year , You should also recite the short answer questions in the two question banks in Baidu online disk that I share （ Link to the first blog in the database ）
Chapter I
1． What is the definition of a database ?
The database is stored in the computer for a long time , organized , A collection of large amounts of data that can be shared .
2. What are the main functions of the database management system
（1） Data definition function ,
（2） Organization of data , Storage and management ,
（3） Data manipulation function ,
（4） Transaction management and operation management of database ,
（5） Establishment and maintenance of database ,
（6） Other functions .
3． What are the three elements of the data model ?
data structure , Data operation and data integrity constraints constitute the three elements of the data model .
4. What are the data operations in the database ?
Data operations in the database include inserting , modify , Delete and query .
5． What are the three types of relationships between entities ?
Relationships between entities include one-to-one relationships , One to many connection and many to many connection .
6． What are the common logical data models in the database field ?
The logical data model commonly used in database field is hierarchical model , Reticular model , relational model , Object oriented model, etc .
7. What are the components of the database system ?
Database system consists of database , Database management system , Application system and database administrator .
8. Three level structure of database system ?
The three-level schema structure of database system refers to external schema , pattern , Internal mode
9. Database management system
Database management system （Database Management
System,DBMS） Is a layer of data management software between the user and the operating system , Provide a method for users or applications to access the database , Including the establishment of database , query , Update and various data control .DBMS Always based on some kind of data model , Can be divided into hierarchical models , Reticular model , relational model , Object oriented model, etc DBMS
10.
Data independence refers to the mutual independence between applications and data , Unaffected . Data independence is divided into physical data independence and logical data independence .（1） Logical independence ： When the mode changes , The database administrator modifies the relevant external schema ／ Pattern mapping , Leave external mode unchanged , So that the application does not have to be modified , Ensure the logical independence of data and program , Abbreviation: logical independence of data .（2） Physical independence ： When the storage structure of the database changes , Database administrator modify mode ／ Inner mode mapping , Leave mode unchanged , Application unaffected . Ensure the physical independence of data and program , Abbreviation: physical independence of data
Chapter II
1. What are the three components of the relational model ?
Relational model consists of relational data structure , Relationship operation and relationship integrity constraints consist of three parts .
2. What are the three types of integrity of relational models ?
The integrity constraints of relationships include primary key constraints , Foreign key constraints and user-defined integrity constraints .
3. Query operations of which relationships are provided in relational algebra ?
Queries in relational algebra include union of relations , hand over , difference , Cartesian product , choice , Projection , Operations such as join and division .
Chapter III
1.SQL What are the commonly used statements in the language ?
SQL Language set data definitions , Data query , Integration of data manipulation and data control functions , The main operation statements include
CREATE,ALTER,DROP,INSERT,UPDATE,DELETE,SELECT,GRANT,REVOKE etc .
2.SQL Which common aggregate functions are available in ? How they are used ?
SQL Some aggregate functions are provided in , Except for statistical database data , include COUNT,AVG,SUM, MAX,MIN etc. ,
COUNT（*） Out of usage , Null values are ignored in Statistics , use DISTINCT Option ignored Statistics on duplicate data . Aggregate functions can only be used with SELECT Clauses and HAVING clause .
3. What is a join query ? How connection queries specify connection conditions ?
If a query involves two tables at the same time , It is called connection query . The connection conditions of connection query can be found in the WHERE Clause is specified by a comparison operation , Or at FROM
Clause specifies both the connection method and the connection condition .
4. What is a subquery ? Used in WHERE There are several ways to call a subquery in a clause ?
Subquery is also called nested query , Is nested in SELECT,INSERT,UPDATE,DELETE Etc of SELECT Query statement . Multi use in
WHERE In Clause , Use the results of subqueries as search criteria . stay Where There are several ways to use subqueries in Clauses ： from IN
Export sub query , Export subquery by comparison operator , from EXISTS Export sub query .
Chapter V
1. What is database integrity ? What are the types of relational database integrity ?
Data integrity refers to the logical consistency and correctness of the data in the database .
Relational database integrity includes entity integrity , Reference integrity and user-defined integrity .
2. The five common constraints are ： Primary key constraint , Foreign key constraint , Non empty constraint , Unique constraint , Check constraints !
Chapter VII
1. What technologies and knowledge are involved in database design ?
Database design involves various technologies and knowledge , Including basic knowledge of computer , Methods and skills of programming , Principles and methods of software engineering , Basic knowledge of database , Knowledge of database design technology and application field .
2. What are the phases of database design ?
Database design including requirements analysis , Conceptual structure design , Logical structure design , Physical structure design , Six stages of database implementation and database operation and maintenance .
3. establish E-R What steps does the diagram include ?
establish E-R The process of drawing includes ：（1） First determine the actual shape ,（2） Determine contact type ,（3） Solid body type And connections E-R chart ,（4） Determine the attributes of entity type and relation
Fill in the blanks in previous years
* The database is stored in the computer for a long time , organized , A collection of large amounts of data that can be shared .
* The functions of the database system include ： Definition of database , Organization, storage and management of database , Manipulation of database , Management and operation management of database affairs , Establishment and maintenance of database
* Manipulation of the database includes inserting , delete , Modification and query
* data structure , Data manipulation and integrity constraints constitute the three elements of a data model
* Exercises between entities include one-to-one connections , One to many contact , Many to many connections
* The logical data model commonly used in database system is hierarchical model , Reticular model , relational model , Object oriented model, etc
* Database system consists of database , Database management system , Application system and database administrator .
* The three-level schema structure of database system refers to schema , Internal mode and external mode .
* Database management system （Database Management System,DBMS） Is located between the user and the operating system
One layer data management software between , Provide a method for users or applications to access the database , Including the establishment of database ,
query , Update and various data control .DBMS Always based on some kind of data model , Can be divided into hierarchical models , Reticular model , relational model , Object oriented model, etc
DBMS.
10. Data independence refers to the mutual independence between applications and data , Unaffected . Data independence is divided into physical data independence And logical data independence .
（1） Logical independence ： When the mode changes , The database administrator modifies the relevant external schema ／ Pattern mapping , Make out mode
remain unchanged , So that the application does not have to be modified , Ensure the logical independence of data and program , Logic of abbreviated data Independence .
（2） Physical independence ： When the storage structure of the database changes , Database administrator modify mode ／ Inner mode mapping , Enable mode protection
Remain unchanged , Application unaffected . Ensure the physical independence of data and program , Abbreviation: physical independence of data .
11. Relational model consists of relational data structure , Relationship operation and relationship integrity constraints consist of three parts .
12. Relationship integrity constraints include primary key constraints , Foreign key constraints and user-defined integrity constraints .
13. Queries in relational algebra include union of relations , hand over , difference , Cartesian product , choice , Projection , Operations such as join and division
14. SQL Language set data query , Data manipulation , Integration of data definition and data control functions , Its main operating language
Sentence includes CREATE,ALTER,DROP,INSERT,UPDATE,DELETE,SELECT,GRANT,
REVOKE etc .
15. SQL Some aggregate functions are provided in , For statistical database data , include COUNT,AVG,SUM,MAX, MIN etc. , except
COUNT（*） Out of usage , Null values are ignored in Statistics , use DISTINCT Option ignored
Statistics on duplicate data . Aggregate rows can only be used for SELECT Clauses and HAVING clause .
16. If a query involves two tables at the same time , It is called connection query . The connection conditions of connection query can be found in the WHERE In Clause Specified by a comparison operation , Or at FROM
Clause specifies both the connection method and the connection condition .
17. Subquery is also called nested query , Is nested in SELECT,INSERT,UPDATE,DELETE Etc SELECT Query statement . Multi use in
WHERE In Clause , Use the results of subqueries as search criteria . stay Where
There are several ways to use subqueries in Clauses ： from IN Export sub query , Export subquery by comparison operator , from EXISTS Export sub query .
18. Database security refers to protecting the database , Prevent data leakage caused by users' illegal use of the database , Change or destroy .
The common security control methods in database systems include user identification and authentication , access control , Define view , audit , number Data encryption, etc .
19. Data integrity refers to the logical consistency and accuracy of data in the database .
Relational database integrity includes entity integrity , Reference integrity and user-defined integrity .
20. trigger （Trigger） It is a kind of special event driven stored procedure defined by the user on the relational table . trigger
Insert table by , Modify and delete event activation .
21. Database design including requirements analysis , Conceptual structure design , Logical structure design , Physical structure design , database
Implementation and database operation and maintenance .
22. establish E-R The process of drawing includes ：（1） First determine the actual shape ,（2） Determine contact type ,（3） Solid body type
And connections E-R chart ,（4） Determine the attributes of entity type and relation
Technology