What is a relational database
The so-called relational database refers to a database that employs a relational model to organize data. The relational model was first proposed by Dr. E.F. Codd, a researcher at IBM, in 1970, and in the decades that followed, the concept of the relational model was fully developed and gradually became the dominant model of database architecture. Simply put, the relational model refers to a two-dimensional table model, and a relational database is a data organization composed of two-dimensional tables and the links between them. The following is a list of commonly used concepts in the relational model.
Relational databases are not the only advanced database model, and they are not at all the most performance-optimized model, but relational databases are certainly the most widely used, easy to understand, and easy to use database model in use today. Most enterprise-level system databases use relational databases, and the concept of relational databases is fundamental to mastering database development, which is why the questions in this section have become one of the frequent questions in .NET interviews.
Relationships: can be understood as a two-dimensional table, each relationship has a relationship name, which is often referred to as a table name.
Tuples: can be understood as a row in a two-dimensional table, often referred to as a record in databases.
Attribute: can be understood as a column in a two-dimensional table, often referred to as a field in a database.
Field: the range of values for an attribute, which is the limit of values for a column in a database.
Keyword: a set of attributes that uniquely identifies a tuple. Often called a primary key in databases, it consists of one or more columns.
Relational schema: refers to a description of a relationship in the format: relationship name (attribute 1, attribute 2, …, attribute N). Often referred to as a table structure in databases.
Advantages of Relational Databases
Relational databases have the following advantages over other models of databases:
Easy to Understand: the two-dimensional table structure is a concept very close to the logical world, and the relational model is much easier to understand as compared to other models such as the mesh and hierarchical.
Easy to use: the common SQL language makes it very easy to operate relational databases, programmers and even data administrators can easily manipulate databases at the logical level without having to understand the underlying implementation at all.
Easy to maintain: rich integrity (entity integrity, referential integrity and user-defined integrity) greatly reduces the probability of data redundancy and data inconsistency.
What is a relational database
A relational database, a database based on a relational model, deals with the data in the database with the help of mathematical concepts and methods such as set algebra. Various entities in the real world and various connections between them are represented by relational models. The relational model was first proposed by Edgar Codd in 1970, along with the “Codd’s Twelve Laws”. Nowadays, although there are some criticisms of this model, it is still the traditional standard for data storage. The standard data query language, SQL, is a language based on relational databases that performs retrieval and manipulation of data in relational databases. The relational model consists of three parts: a relational data structure, a collection of relational operations, and relational integrity constraints.
Simply put, a relational database is a database consisting of multiple two-dimensional row and column tables that can be linked to each other.
Introduction to relational databases
The relational model refers to the two-dimensional table model, and thus a relational database is composed of two-dimensional tables and their links between the composition of a data organization. The current mainstream relational database Oracle, DB2, MicrosoftSQLServer, MicrosoftAccess, MySQL, Wave K-DB and so on.
Entity-RelationshipModel (Entity-RelationshipModel), referred to as E-RModel is a set of database design tools proposed by Dr. P.S. Chen (PeterP.SChen) in 1976, he used the concept of things and relationships in the real world to explain the abstract data architecture in the database. The Entity-Relationship Model utilizes a graphical approach (Entity-RelationshipDiagram) to represent the conceptual design of a database, which facilitates conceptualization and communication discussions during the design process.
Why is it called “relational database”
Haha, table database.
Relational, of course, is about the relationship between the table, interdependence, to reduce redundancy, for example: primary and foreign key relationships
In order to compound the design of the database so-called three paradigms, and so named. For large amounts of data is necessary, a string is not much, but if the massive data, it is very occupied hard disk space, is not conducive to the deployment of transfer.
Three database paradigms to understand:
The first paradigm: http://ke..com/view/176725.htm
The second paradigm: http://ke..com/view/176736.htm
The third paradigm: http://ke..com/ view/176738.htm
In order to create less redundant and well-structured databases, there are certain rules that must be followed when designing a database. In relational databases such rules are called paradigms. A paradigm is a summary that meets a certain design requirement. To design a well-structured relational database, certain paradigms must be met.