C++ const members and static members

const members and static members Cont members of class const data members Const data members can only be initialized through a constructor initializer list. class Box {<!– –> private: const int length; //Length const int width; //width const int height; //height public: Box(); Box(int H, int W, int L); }; Box::Box(int H, int W, int […]

MySQL constraints & special queries

MySQL Constraints & Special Queries Article directory MySQL Constraints & Special Queries 1. Database constraints 1.1 Constraint types 1.2 NULL constraints 1.3 NUIQUE: unique constraint 1.4 DEFAULT: Default value constraints 1.5 PRIMARY KEY: Primary key constraints 1.6 FOREIGN KEY: foreign key constraints 1.7 CHECK constraints 2. Relationship between tables 2.1 One-on-one 2.2 One-to-many 2.3 Many-to-many […]

1. Hadoop3.1.3 cluster construction

1. Cluster planning hadoop01(209.2) hadoop02(209.3) hadoop03(209.4) HDFS NameNode DataNode DataNode SecondaryNameNode DataNode YARN NodeManager ResourceManager NodeManager NodeManager Do not put NameNode and SecondaryNameNode on the same server 2. Create user useradd atguigu passwd *** Configure atguigu user permissions vim /etc/sudoers ## Allow root to run any commands anywhere root ALL=(ALL) ALL ## Allows people in […]

Vue CLI scaffolding installation, construction, configuration and CLI project analysis

Table of Contents 1. Quick Start with CLI 1. Official introduction: 2. Install Vue CLI: 3. Build Vue CLI: 4.IDEA configures Vue CLI: 2. Vue CLI project analysis 1. Structural analysis: 1.1 config 1.2 node_modules 1.3 src 1.4 static 2. Process analysis: 2.1 main.js 2.2 router/index.js 2.3 components/HelloWorld.vue 2.4 App.vue 2.5 index.html 1. Quick Start […]

Why use virtual environment in python? (Virtual environment function and virtual environment construction, switching, exit, migration and packaging) code demonstration. Official venv usage (**)

Detailed graphic and text explanation of python’s virtual environment (virtual environment functions and virtual environment construction, switching, exit, migration and packaging) code demonstration https://blog.csdn.net/weixin_45440484/article/details/130144943 http://www.360doc.com/content/23/0828/21/1339386_1094251670.shtml Why use a virtual environment? First, a virtual environment helps keep your projects clean and separate. You don’t have to worry about one project’s dependencies breaking another, which makes project […]

Hadoop 3.3.6 distributed cluster environment construction

1 System Configuration A total of 3 centOS virtual machines have been prepared, master, slave1, slave2 Configure hosts resolution vim /etc/hosts master slave1 slave2 Modify hostname #Execute the following commands on the corresponding server hostnamectl set-hostname master hostnamectl set-hostname slave1 hostnamectl set-hostname slave2 Turn off firewall #Close firewall systemctl stop firewalld.service #Disable […]

ZooKeeper+Kafka+ELK+Filebeat cluster construction to realize large batch log collection and display

The general process: After collecting the logs of the nginx server (web-filebeat) through filebeat, store them in the cache server kafka, and then logstash to the kafka server to retrieve the corresponding logs. After processing, they are written to the elasticsearch server and displayed on kibana. 1. Cluster environment preparation 4c/8G/100G Kafka + ZooKeeper […]

Database integrity – entity integrity, referential integrity, attribute constraint naming clauses, domains

Article directory Database integrity 1. Entity integrity 1. Define entity integrity 2. Entity integrity check and breach handling 2. Referential integrity 1. Define referential integrity 2. Reference integrity check and default conditions 3. Constraints on attributes 1. Definition of constraints on attributes 2. Inspection of constraints on attributes and handling of breaches 4. Integrity constraint […]

Raspberry Pi 4B system construction (Raspberry)

1. Construction preparation 1. Download the Raspberry Pi system download link: Operating system images – Raspberry Pi /icon-default.png?t=N7T8″ alt=”icon-default.png?t=N7T8″>https://www.raspberrypi.com/software/operating-systems/#raspberry-pi-os -legacy Operating system images – Raspberry Pi /icon-default.png?t=N7T8″ alt=”icon-default.png?t=N7T8″>https://www.raspberrypi.com/software/operating-systems/#raspberry-pi-os -legacy Find here and click the first one. Since the latest system cancels the default username and password login, the latest system must use an external display […]