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[summary] if the server where CentOS is located is limited to security reasons and the customer does not configure us to access the Internet, how to install the PostgreSQL database? This article will explain in detail how to install PostgreSQL12 database offline on CentOS7 system through specific steps. 1 offline installation package preparati ...

1, Annotation development 1.1 comparison between annotations and xml xml: as a configuration file Advantages: it can extract content (decoupling), clear configuration, convenient positioning and easy to findDisadvantages: complicated configuration Note: xml development can be replaced Advantages: fast development speed and no cumbersom ...

architecture design We can divide the functional architecture of Mybatis into three layers: API interface layer: interface APIs provided for external use. Developers use these local APIs to manipulate the database. As soon as the interface layer receives the call request, it will call the data processing layer to complete the specific da ...

mybatis supports different databases. The specific access to the database is the driver jar package provided by different database manufacturers. For example: mysql-connector-java.jar of MySQL The jar s provided by different manufacturers are also implemented based on the interface in the java.sql package under the JDK For example, different d ...

2, Mycat global serial number Mycat can guarantee id uniqueness in the following ways: 1) Local file mode 2) Database mode 3) Timestamp mode 4) ZKID generator 5) ZK increment ID 4 and 5 are recommended In the above 5 methods, the global serial number configuration should be enabled in the server.xml file and the autoIncrement attribute of the l ...

Django's operation on the database (addition, deletion, modification and query) 1. Add data 1.save method >>>from entry name.models import Table name to import >>>Variable name = In which table do you want to add the name of the data table( Added data,for example:name = 'Xiao Ming', age = '18' ) >>>Variable ...

MySQL Learning Notes Log on and exit MySQL server # Log in to MySQL $ mysql -u root -p12345612 # Exit MySQL database server exit; Basic Grammar -- Show all databases show databases; -- Create a database CREATE DATABASE test; -- Switch database use test; -- Show all tables in the database show tables; -- Create Data Table CREATE TABLE ...

1, Importance of data backup In a production environment, data security is critical Any loss of data can have serious consequences Causes of data loss Program error Human operation error Operation error disk failure Disasters (e.g. fire, earthquake) and theft 2, From a physical and logical point of view, backup can be divided into Physic ...

Answer #11: what is the difference between char and varchar in MySQL 1. Experimental scenario GreatSQL 8.0.25 InnoDB 2. Experimental test 2.1 differences parametercharvarcharIs the length variableFixed lengthLengthenstorage capacity 0 ~ 2550 ~ 65,535 2.2 construction test table CREATE TABLE vc (v VARCHAR(4), c CHAR(4)); 2.3 test without ...

Mybatis inserts multiple records using the @ Insert annotation Several methods of converting JSONObject to List In a large software engineering job, if an administrator wants to send messages to multiple users, the front end needs to send an array with user numbers to the back end. Here is a summary of several methods for the back-end to rece ...