1- database understanding

1. What is a database

    Database is organized according to data structure 、 Warehouse for storing and managing data .

2. What is a relational database management system （RDBMS）

    A relational database is a database based on a relational model , With the help of set algebra and other mathematical concepts and methods to deal with the data in the database .

    The associated database management system saves the data in different tables , Instead of putting all the data in one big warehouse , This increases speed and flexibility .

3. The characteristics of relational database management system （RDBMS）

1. Data is presented in tabular form
2. Name of each record
3. Each column is the data field corresponding to each record name
4. Many rows and columns make up a form
5. Several forms make up DataBase

• database ： A database is a collection of related tables
• Data sheet ： A table is a matrix of data .
• Column ： A column of data elements contains the same data
• That's ok ： A row is a group of records , It's a set of related data
• redundancy （rong, three ）： Store twice as much data , Reduced performance but improved data security
• key ： The value of the key is unique in the current table
• Primary key ： The primary key is unique . A data table can only contain one primary key . You can use the primary key to query data
• Foreign keys ： Foreign keys are used to associate two tables
• Composite key ： Composite key （ Composite key ） Use multiple columns as an index key , Generally used for Composite Index
• Indexes ： Use indexes to quickly access specific information in database tables . An index is a structure that sorts the values of a column or columns in a database table .
• Referential integrity ： Referential integrity requires that nonexistent entities cannot be referenced in a relationship .