One, MySQL database
1. The concept of database
1.1 Why do we have a database
> The previous arrays, collections, etc., when the program is closed, the data we need is directly recovered by the JVM. When we store the data in the database, the data will not be lost after the program is closed. Therefore, we have a database.
1.2 The concept of database
>Database is an effective technology for data management. It is an ordered collection of a batch of data, which is stored in a structured data table. The data tables are related to each other, reflecting the essential connection between objective things. The database can effectively help an organization or enterprise to scientifically manage all kinds of information resources.
>Data is the basic object stored in the database, which is a physical symbol arranged and combined in a certain order. There are many manifestations of data, which can be numbers, text, images, and even audio or video. They can all be digitized and stored in a computer.
>Database is a collection of data with a unified structure and stored in a unified storage medium. It is an integration of multiple application data and can be shared by various applications.
1.3 Common Concepts of Database
>DB database (database): the "warehouse" for storing data. It saves a series of organized data.
>DBMS Database Management System (Database Management System). Data is a container created and manipulated by DBMS
>SQL structured query language (Structure Query Language): a language specifically used to communicate with the database
Advantages of SQL:
a. It is not a proprietary language of a particular database vendor, almost all DBMS support SQL
b. Easy to learn
c. Although simple, it is actually a powerful language. Using its language elements flexibly, it can perform very complex and advanced database operations.
1.4 Common database systems are:
MySQL 、 Oracle 、 DB2 、SqlServer等
1.4.1 The advantages and disadvantages of common database systems:
>Oracle:
>Advantages: good portability (applicable to all kinds of large, medium, small and microcomputer environments), easy to use, and powerful
> Disadvantages: high cost, general enterprises will not use
>DB2:
>Advantages: Good parallelism, high security, cross-platform, multi-layer structure
> Disadvantages: DB2 handles massive amounts of data, and the average enterprise cannot reflect the advantages of DB2
>SqlServer：
>Advantages: High scalability, wide ecological chain
>Disadvantages: still have to meet the requirements of related software and hardware
>MySQL:
>Advantages: low cost, open source, cross-platform, freedom (can be used in most application scenarios)
> Disadvantages: small scale, limited functions
1.5 Features of the database:
> Put the data in the table, and then put the table in the library
> There can be multiple tables in a database, and each table has a name to represent itself. It is unique.
> Table has some characteristics, these characteristics define how the database is stored in the table, similar to the design of "class" in Java.
>The table is composed of columns, which we also call fields. All tables are composed of one or more columns, and each column is similar to "attributes" in Java.
> The data in the table is stored in rows, and each row is similar to an "object" in Java.
1.6 DBMS is divided into two categories:
-DBMS (Access) based on shared file system
-Based on client-server DBMS (MySQL, Oracle, SqlServer)