Introduction to database - Introduction to database

Introduction to database related foundations

Hello everyone , This time I bring you my new column ： database , The database is relatively not that difficult , As long as you practice hard 、 Memorize grammar , I believe that learning database well is not a problem , Bloggers will start from 0 analyse , Explain the knowledge points of database step by step , And will give many examples . most important of all , Bloggers will not use software , Use the most primitive way -> Command line to explain , The advantage of this explanation is to write sentence by sentence , It won't cause the problem that readers can't keep up with their ideas ！

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1、 Introduction to database

1.1 What to learn from database ?

1. Basic operation of database ( With SQL Statement is the core ),SQL Is a programming language , It's easy to use
2. The underlying principle of database ( Mainly for common interview questions )
3. Database programming ( Use Java Language operation database )

1.2 What is a database ？

Database is a software ( One kind of software ), This kind of software function is ” Management data ”, Software that organizes and stores data

1.3 Relationship with data structure

database ： Software

data structure ： Discipline

Database software in the implementation process , Is very dependent on data structures , Realize the internal management of database software , It will be widely used in various data structures ～

The subject of data structure is discussing how to organize and manage data ～ The purpose of management is to ” Additions and deletions ”

1.4 classification

1.4.1 Relational database

1. Definition ： The organizational form of data is “ surface ” As a structure , Be similar to excel. First of all, there must be ⼀ Multiple headers , There are many columns in the header , And every ⼀ The type of the column , The inserted data is a row in the table . Everyone in this line ⼀ Columns need to correspond to the header structure .

   

2. For data “ constraint ”（ Verification of data legitimacy ） Relatively strong

3. Suitable for most scenarios MySQL,Oracle,SQL Server,SQLite

1.4.2 Non relational database

1. Non relational database （ Also called NoSQL）： The organizational form of data is “ Key value pair ” As a structure . Be similar to Map
2. When storing, it is necessary to formulate key and value, Of each group of data value Which fields should be included in , There is no explicit requirement , Lower constraints on data
3. Compared with relational databases , sacrificed ⼀ Part of the function , But in exchange for higher efficiency and stronger horizontal expansion ability It is more suitable for distributed systems

1.5 The basic components of a computer （ Digression ）

1. External storage ： Divided into floppy disks 、 Hard disk 、 Compact disc 、 Hard disk 、U disc （flash）, Hard disks and U disc

2. The difference between memory and external memory ：

   1. Memory has less storage space (8G,16G), The storage space of external memory is large (512G,1T)

   2. Memory access speed is fast , The access speed of external memory is slow ( Probably worse 3-4 An order of magnitude )

      The external memory here refers specifically to the mechanical hard disk , Hard disk also includes mechanical hard disk and SSD, Mechanical hard disk is limited by the physical structure of mechanical hard disk , Cause his storage speed , It has not developed for nearly ten years . however SSD Solid state disk access speed is very fast , Much faster than mechanical hard disk , The best solid state drive , It's almost catching up with the most garbage memory ～ But in general SSD It will be much slower than memory

   3. Memory costs are high , Low cost of external storage

   4. Data in memory disappears after power failure , The data in the external memory is still after power failure

      It's not absolute . But generally, the storage time of mechanical hard disk storage data is a few years ~ More than ten years

3. Most computers in the world today (99% above ) It is built according to the above structure ～

1.6 The granddaddy ： Von Neumann and Turing ( Digression )

Tell you about the glorious history of the two grandparents

Part I： Von Neumann

Von Neumann architecture , be called “ Von Neumann ” The big guy put forward , Can be said to be 20 The century is the most NB All in all , It is a mathematician , Or physicists , Or a chemist , Father of computer , In World War II , Also participated in the Manhattan Project , They came together to study the atomic bomb .

At the age of , one day , Boss von Neumann , Go by train ～（ Green car ）, There is a guy on the opposite side “ A researcher at Princeton University ”, Study one for ” Computing machine “, But there are some bottlenecks , I can't get it down ～～～ Boss von Neumann went for a walk , For some time , He took the lead in the research of the first generation of computers ！

Computers use binary , It was also put forward by boss Feng ～

Part II： Turing

Turing laid the theoretical foundation of computer

Turing also participated in World War II ～ The greatest contribution , Cracked the German telegraph encryption system , This directly promoted the Normandy landing

But unfortunately, he died young ～ It is said to have received persecution from the British royal family ～

1.7 Storage location

In general ,MySQL The data of is saved on the hard disk ～ (” Persistent storage “ The way ), But there are also a few databases , It stores data in memory ( such as :Redis,Tair…)

So in the actual large-scale development , The most prone to problems , Database .

by comparison , The data structure we learned before ～ Especially the code written before , Data is basically stored in memory ～（ Variables created in code , Save it to the corresponding memory space ）

1.8 Introduction to common database software

1. Oracle: The best database , Beyond all doubt

   The best database Namely Oracle, No ⽤ His reasons ： your ！ Ordinary students can't afford ,⼀ Some small and medium-sized companies can't afford , Even some big factories can't afford it , Those who can really afford it are the rich and powerful financiers , Such as banks .

   Characteristics of banks ：

   1. Data is particularly important
   2. Not bad money

   Your main thing is not the use of software , Instead, you spend money on ⼀ Peace , don 't worry , But also ⼀ A pot bearer （ Something's wrong, someone's lying ）, Something went wrong. Oracle The technology of

   Support will provide on-site service , So what you spend money on is service .

   by comparison MySQL It is more suitable for us , Free open source , Whoring for nothing ⼀ Shi Shuang , Have been whoring for nothing ⼀ Straightforward ～

   and ,Oracle Basically, it needs to run on a computer with ultra-high configuration ！( To exaggerate , Only national computers are suitable for use )

2. MySQL： Free open source , The user experience is also very good

   At home , At the very beginning ,MySQL Our market share is very low , Or to Oracle Mainly

   Alibaba takes the lead , Set off ⼀ site “ Go to Oracle” The revolution of . at that time MySQL yes ⼀ An alternative , Alibaba was also developing its own database at that time

   At the beginning of the replacement , Many problems , Fortunately, countless bigwigs have come one after another , Step on the pit and fill it ,MySQL Also experienced ⼀ A rapid development process . Final
   MySQL It's relatively stable and funny , It is called the current very mainstream database .

   however MySQL High speed development of , Also grabbed a lot Oracle Market share .

   Oracle To contain MySQL The development of , a fundamental solution , to MySQL bought , Immediately after buying MySQL No more open source （ Although it is still free for the time being ）

   meanwhile Oracle It's also Java Dad

   Oracle This company is particularly fond of doing things ～

   Google The whole year Android, I wanted to use Python. At the right time Python My father left Google , Google switched the language to Java.

   With Android From wind to water , Everyone is jealous of what they don't want ,Oracle At this time, an idea occurred , Just put Java I bought it , then Oracle Just Google

   Went to court , If you want to use Java Develop Android , You have to pay （ Blackmail ！） Google lost , Only lose money

   So Google is angry and ready to develop ⼀ Generation mobile terminal system , Development language carried ⾔Dart（ Google self-developed language ⾔）, Equipped frame Flutter etc. .

   here MySQL The author is also angry ,Oracle The company searches , References to . So he used to MySQL Based on the open source version of ⼀ Branches , It's called

   Mariadb, It is still open source and free .Mariadb And the original MySQL Are compatible with each other , It's OK to use any one in your current study

3. SQL Server: Pretty good also , Marketing strategies hurt him

   SQL Server Database produced by Microsoft
   It's actually ⼀ A very good and powerful database , But no one used it
   The main reason ：

   1. Rechargeable , And it's not too cheap
   2. In the early SQL Server and Windows The platform is bundled , But at that time, the mainstream server systems were Linux
      Because of this marketing mistake , Leading to the loss of market share
      SQL Server The market share of is MySQL Take over
      C# Its market share has also been Java Take over
      Then Microsoft reacted , Adjustments have also been made , Give Way SQL Server and C# can ⽀ Cross platform , But it's too late

4. SQLite: The largest installed database in the world

   Android phone comes with its own database , Small and light

There are other databases , such as SQLite,HBase,MongoDB,Redis wait

Later in practical work , The most used database , still MySQL, Between databases , Not much difference ,“ By knowing one method you will know all ”