Final review of Database Principles

The first 1 Chapter
The introduction
database （DB)： It is the aggregation of database data , And the data in this collection must be able to be managed by the computer and shared by multiple users
Database management system （DBMS): It is a large-scale software for manipulating and managing databases , It consists of a set of computer programs
Database system （DBS）： By hardware and software 、 The database and users together constitute . Hardware is mainly used to store data in the database , Including computers 、 Storage devices, etc . The software part mainly includes the database management system 、 An operating system that supports the operation of a database management system , And support the access technology of multi language application development .
A complete database system generally consists of databases 、 Database management system 、 Application development tools 、 Application system 、 Database administrators and users .

The database system mainly includes the following 3 Components ：
database ： A place for storing data .
Database management system ： Software for managing databases .
Database applications ： In order to improve the processing capacity of the database system, the software used to manage the database is supplemented .

database （DataBase,DB） It provides a storage space to store all kinds of data , You can think of a database as a container for storing data . A database may contain many files , A database system usually contains many databases .

Database management system （Database Management System,DBMS） It's user creation 、 The software used to manage and maintain a database , Between the user and the operating system , Unified management of the database .DBMS Can define data storage structure , The operation mechanism of providing data , Maintain database security 、 Integrity and reliability .
Database applications （DataBase Application） The use of data management can meet the higher requirements of data management , It can also make the data management process more intuitive and friendly . The database application is responsible for working with DBMS communicate 、 Access and management DBMS Data stored in , Allow users to insert 、 modify 、 Delete data from database .

Characteristics of database system ： Data structure 、 Low data redundancy 、 High sharing 、 Avoid data inconsistency 、 High data independence 、 from DBMS Unified management and control （ Security 、 integrity 、 concurrency control 、 Database recovery ）

Data model ：
Refers to the simulation and abstraction of real-world data and information , Used to describe data 、 Compose data and operate on data
classification ： Conceptual data model 、 Logical data model 、 Physical data model
Components ： data structure 、 Data manipulation 、 Data integrity constraints

Square box ： Entity set
Diamond frame ： contact
Elliptical box ： attribute

Three level pattern structure ： External mode 、 Conceptual model 、 Internal mode （ A database can have multiple external schemas 、 A database can only have one internal schema
Two level image ： External mode image 、 Inside ~

The first 2 Chapter
relational database
Domain ： Is a set of values with the same data type
code ：
It consists of one or several attributes
Candidate code : In a relationship , Attribute or minimum attribute set that can uniquely identify tuples
Main code ： There are multiple candidate codes in a relationship, choose one as the main code
Outer code

Relationship integrity constraints ： Using integrity constraints is to use integrity rules to constrain the relationship
The values of the two main codes are unique in the table 、 affirmatory , All attributes of the specified relationship on the master code cannot be null , Instead, the main code as a whole cannot be null
Entity integrity ： The primary code is unique and not empty
Referential integrity ： The outer code is either empty , Or corresponding to other table main codes
User defined integrity ： Write it completely

The cartesian product ：
Inquire about ：

Natural join ：

The discarded ones are called floating tuples
except ：

The first 3 Chapter
Relational database standard language SQL
SQL characteristic ： Highly unprocessed 、 Fully functional and integrated 、 Unified grammatical structure 、 The language is simple , Easy to learn and easy to use
SQL Define functions ：
The definition of the table :
create table Table name （ Various attributes );

create table user(
name varchar(20),
age int
)

Delete
CASCADE For foreign key

drop table student CASCADE

Change

alter table student alter column sage int; 

Inquire about
id,title Modifiable name

select *from student;

selsct *from user where id=9 and password=123;

The results were de duplicated

selsct distinct title  Course name  from edu_course;

Add conditions to the query results

selsct title  Course name  from edu_course where price between 10 and 999;

% Can represent multiple characters , Underline _ Representing one
group by grouping , Screen selection having
For equivalent connection where

select *from edu_course ec,edu_course_description ecd where ec.id=ecd.id;

Check the total number of students

select count(*) as  The total number of 
from  Student ;

Check the average age of computer college students

select avg(year(now))- Year of birth ） as  Average age 
from  Student 
where  college =' Computer '

Inquiry learning 180101 The highest score of students in course No

select max( achievement ） as  The highest 
from  Study 
where  Course no. ='180101'

Check options 180102 Student ID and grade of course No , The results are ranked from high to low

select  Student number , achievement 
from  Study 
where  Course no. ='180102'
order by  achievement  desc

Composite conditional join query
Check options 180101 And the grade is in 90 The student number of the above students , Name and grade

select  Student . Student number , full name , achievement 
from  Student , Study 
where  Student . Student number = Study . Student number 
and  Study . Course no. ='180101'
and  Study . achievement >90

nested queries

select  full name 
from  Student 
where  Student number  in
(select  Student number 
from  Study 
where  Course no. ='180101');

Insert a single tuple

insert
into  Student 
values('111',' Xia Yu ',' male ',' Computer '）;

Insert subquery results

insert
into dept_age(sdept,avg_age)
select  college ,avg(year(now())- Year of birth ）
from  Student 
group by  college 

Delete

delete
from  Student 
where  Student number ='092010';

Change

update  Student 
set  Place names =' jiangsu '
where  Course no. ='1111'

Modification of subquery

update  Study 
set  achievement =0
where  Student number  in
(select  Student number 
from  Student 
where  college =' Computer '）;

View ：

create view cs_view
as select *
from  Student 
where  college =' Computer ';

Delete view

drop view < View name >

Query view

select *
from cs_view
where year(now())- Year of birth <20;

Update the view
Insert 、 Delete 、 modify

The first 4 Chapter
Relationship normalization theory
Function dependency ：

Functional dependence of code ：
In relation mode R in , A set that uniquely determines the minimum attributes of a tuple
if X Sole determination Y, be XY There is a functional relationship between
set up K by R<U,F> Properties or property groups in , if K–f—>U, be K by R The candidate code for , There are more than one candidate codes. Choose one of them as the main code

Normal form to BC normal form ：


Closure ：


Code value theory ：

Armstrong axiom


rely on ：

Minimum dependence ：

The first 6 Chapter
Database protection
Business ：
It is to package a group of database operations to form a logically independent work unit , This unit of work is indivisible , The database operations included in it either all occur , Or none of it will happen
characteristic ： Atomicity 、 Uniformity 、 Isolation, 、 persistence
Database recovery ：
Fault type ： Transaction internal failure 、 System failure 、 Media failure 、 Computer virus
implementation technique ： Establish redundancy through data dump 、 Establish redundancy through log files 、 Fault recovery