Skip to content

Latest commit

 

History

History
92 lines (62 loc) · 2.63 KB

database_system_concept_1.md

File metadata and controls

92 lines (62 loc) · 2.63 KB
Raw

database system 读书笔记 1

ch01-ch02

current process

2.3 Database Schema, page 44

快速选中沙拉查词/firefox 的 pdf 阅读器进行反色

inspect($$('#viewerContainer')[0])

relational algebra review

relational algebra 学术上用于无重复的数据集合/records，但现代数据库允许表中有重复行，因此可以推广到

operator Greek letter SQL notes
select sigma(σ) WHERE predicate and(∧) or(∨) not(¬)
projection pi(Π) SELECT
Cartesian-product cross(x) CROSS JOIN
join ⋈
rename rho(ρ) AS

set operation

  • union
  • intersection
  • except

words

  • obtained 48 patents: 拥有 48 项专利
  • bibliographical: 书目信息
  • exploit: 利用
  • sophisticated: complex
  • payroll: 工资表
  • ubiquitous: 无所不在
  • cybersecurity: 网络安全

typos: indexes -> indices

misc

constraint can be an arbitrary predicate(谓词) pertaining(与..关联) to the database

Data dictionary, which stores metadata about the structure of the database, in particular the schema of the database

query optimization

picks the lowest cost evaluation plan from among the alternatives

ch2 (divider)

DDL/DML/DQL

  • DDL: CREATE/DROP/ALTER
  • DML: INSERT/DELETE/UPDATE, Procedural/Declarative/nonprocedural(当今主流，数据库自动生成执行计划) DML
  • DQL: SELECT

terms

relation instance

term relation instance to refer to a specific instance of a relation,

that is, containing a specific set of rows. The instance of instructor shown in Figure 2.1

has 12 tuples, corresponding to 12 instructors.

tuple and attribute

  • relations == table
  • tuple == row
  • attribute == field/attribute
  • domain == attribute/字段 的可选值(a set of permitted values)
    • a domain is atomic: 字段是单个值，字段的值不是数组 ~~ atomic domain 相当于 unique 吧 ~~

A relationship between n values is represented mathematically by an n-tuple of values, that is, a tuple with n values, which corresponds to a row in a table. Thus, in the relational model the term relation is used to refer to a table, while the term tuple is used to refer to a row. Similarly, the term attribute refers to a column of a table.

snapshot

  • database schema: logic design of database
  • database instance: a snapshot of the data in the database

superkey

  • superkey: 主键或者复合主键
  • candidate keys/primary_key: superkey's and its subsets only one superkey 也就是单个主键的意思，或者是复合主键但去掉任何一个复合主键tuple成员都会无法构成 pk