Three paradigms of databases

Introduction to three database paradigms: 1. first paradigm: In any relational database, 1NF is the basic requirement for the relational model. databases that do not meet 1NF are not relational databases. The first paradigm (1NF) means that each column in the database table is an inseparable basic data item. There cannot be multiple columns in the same column, that is

Introduction to three database paradigms: 1. first paradigm: In any relational database, 1NF is the basic requirement for the relational model. databases that do not meet 1NF are not relational databases. The first paradigm (1NF) means that each column in the database table is an inseparable basic data item. There cannot be multiple columns in the same column, that is

Introduction to three database paradigms:

1. First paradigm: In any relational database, 1NF is a basic requirement for the relational model. databases that do not meet 1NF are not relational databases.

The first paradigm (1NF) means that each column in the database table is an inseparable basic data item. The same Column cannot contain multiple values, that is, an attribute in an object cannot have multiple values or duplicate attributes.

In short, the first paradigm is that each table has no duplicate columns.

2. Second paradigm: the second Paradigm (2NF) is established on the basis of 1NF, that is, to satisfy the second Paradigm (2NF) must satisfy the first paradigm (1NF ).

The second Paradigm (2NF) requires that each instance or row in the database table be able to be distinguished by a unique region. To implement differentiation, you usually need to add a column to the table to store the unique identifier of each instance.

This unique attribute column is called as the primary keyword, primary key, and primary code.

In short, the second paradigm is that each table has a primary key.

3. Third paradigm: satisfying the third paradigm (3NF) must first satisfy the second Paradigm (2NF ).

The third paradigm is that attributes do not depend on other non-primary attributes. Database tables that conform to the third paradigm are orthogonal and complete.

In short, the third paradigm (3NF) requires that a database table do not contain information about non-primary keywords already contained in other tables.

In practical applications, most relational database tables are designed as follows:

The basic table should conform to the third paradigm, that is, the table has a primary key and no redundant fields.

Some common business tables have some redundancy (repeated addition of non-primary attributes in some basic tables ), this aims to improve the performance and efficiency of Multi-Table cascade queries and discard the limitations on the third paradigm.

Therefore, in general, the database design is between the second paradigm and the third paradigm.