添物零基礎到大型全棧架構師 不花錢學計算機及編程（預備篇）— 數據庫

數據庫就是寄存數據的倉庫。

為何要學習數據庫？

為了開發的方便，大家基本使用統1數據庫進行數據的存儲盒檢索。

SQL是甚么？

SQL（Struct Query Language）是1標準，大家用來統1數據庫操作使用的。比較簡單和方便使用。

數據庫學習使用Windowds系統的可以用微軟SQL Server進行實戰，如果用Linux的話，就使用MySQL吧。Oracle和DB2就是高級點而已，1般互聯網公司也不用，也就是電信和銀行等巨頭使用。

參考視頻學習網站：

1.SQL教程 （楊中科）使用微軟SQL Server講授的。

2.MySQL數據庫（高洛峰）

3.尚學堂馬兵士Oracle視頻教程

參考圖書：

學哪一種數據庫可以選擇其對應圖書，也有些圖書是通用的。有點經驗再買也能夠，1般官方文檔就是最好的學習資料了。

《Head First SQL》像看圖畫書1樣學習SQL，Head系列都還可以。

《Teach Yourself SQL in 21 Days》是非常不錯的學習教程。

《SQL必知必會(第3版)》也不錯，1般多版的圖書都不會差，好才會有需求。

參考學習：

SQL in 24 Hours

強烈推薦此書：《Transact-SQL權威指南》

SQL必知必會也能夠

如何衡量學習效果？

Oracle是可以考證的，其他的我不知道。

必須掌握和了解的基本概念（包括單不限于）

DataBase／DB／表／行／列／視圖／字段／字段類型／數據長度／SQL／存儲進程／ACID／觸發器／連接查詢／左連接／右連接／內連接／外連接／管理系統／用戶／用戶權限／數據庫系統管理員／備份／恢復／日志／查詢分析等

Edgar F. Codd  12 rules

Rule 0: The Foundation rule:

For any system that is advertised as, or claimed to be, a relational data base management system, that system must be able to manage data bases entirely through its relational capabilities.

Rule 1: The information rule:

All information in a relational data base is represented explicitly at the logical level and in exactly one way — by values in tables.

Rule 2: The guaranteed access rule:

Each and every data (atomic value) in a relational data base is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.

Rule 3: Systematic treatment of null values:

Null values (distinct from the empty character string or a string of blank characters and distinct from zero or any other number) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type.

Rule 4: Dynamic online catalog based on the relational model:

The data base description is represented at the logical level in the same way as ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data.

Rule 5: The comprehensive data sublanguage rule:

A relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and that is comprehensive in supporting 

all of the following items:

1.Data definition.

2.View definition.

3.Data manipulation (interactive and by program).

4.Integrity constraints.

5.Authorization.

6.Transaction boundaries (begin, commit and rollback).

Rule 6: The view updating rule:

All views that are theoretically updatable are also updatable by the system.

Rule 7: High-level insert, update, and delete:

The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update and deletion of data.

Rule 8: Physical data independence:

Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.

Rule 9: Logical data independence:

Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit unimpairment are made to the base tables.

Rule 10: Integrity independence:

Integrity constraints specific to a particular relational data base must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.

Rule 11: Distribution independence:

A relational DBMS has distribution independence.

Rule 12: The nonsubversion rule:

If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher level relational language (multiple-records-at-a-time).

CAP理論（散布式系統）

又稱CAP定理，指的是在1個散布式系統中， Consistency（1致性）、 Availability（可用性）、Partition tolerance（分區容錯性），3者不可得兼。

散布式系統的CAP理論：理論首先把散布式系統中的3個特性進行了以下歸納：

   1致性（C）：在散布式系統中的所有數據備份，在同1時刻是不是一樣的值。（同等于所有節點訪問同1份最新的數據副本）

   可用性（A）：在集群中1部份節點故障后，集群整體是不是還能響應客戶真個讀寫要求。（對數據更新具有高可用性）

   分區容錯性（P）：以實際效果而言，分區相當于對通訊的時限要求。系統如果不能在時限內達成數據1致性，就意味著產生了分區的情況，必須就當前操作在C和A之間做出選擇。

再介紹幾個高級內容

數據倉庫

簡單講就是寄存數據的倉庫，形象點就是大的數據庫。

數據分析

SQL基礎必備。

數據發掘

1般也有SQL的使用。

NOSQL

MongoDB

云

Hadoop，Cassandra，HBase等

總結

實際工作中不完全依照書本上的模式走，完全可以不按范式規范。

致敬：Edgar Frank Codd

Codd提出了1個新的解決方案。在終究搜集到1970年具有創新性的技術論文--A Relational Model of Data for Large Shared Data Banks（大型同享數據庫的關系數據模型）中的1系列報告中，Codd建議將數據獨立于硬件來存儲，程序員使用1個非進程語言來訪問數據。Codd的解決方案的關鍵，是將數據保存在由行和列組成的簡單表中，而不是將數據保存在1個層次結構中。

依照Codd的想法，數據庫用戶或利用程序不需要知道數據結構來查詢該數據。發表了該論文以后不久，Codd又發布了更加詳細的指點原則，提出了其指點創建關系數據庫的12項原則。 

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