Relational model:
Relational Query Language<--->Relational Algebra<--->Data<--->Constraints 约束
Relational model is based on Set Theory 集合论 and Predicate Logics(First Order Logics)
Set Theory 表示数据是没有顺序的
Relational DBMS:
Users<--> Applications&Utilities<--->Relational DBMS<--->Relational Database
OLTP(On-Line Transaction Processing)联机事务处理数据库:
MariaDB、MySQL、PostgreSQL、SQLite、HBase、cassandra
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OLAP(Online Analytical Processing) 联机分析处理 数据库:
Hive、impala、tajo
Keys
- Superkey
Let K⊆R, K is a superkey of R if values for K are sufficient 充足的 to identify a unique tuple of each
possible relation R.
example: {ID} and {ID,name} are both superkeys of instructor
- Candidate Key
Superkey K is a candidate key if K is minimal
Example: {ID} is a candidate key 候补者 for Instruct
- Primary key