node. How to implement the SQL statement after JS connects to the database?

node.js Connect to database

These three things should be done well before using ：

1、 Create an empty folder using Vscode open , Next, input npm init Initialize it
2、 install mysql Plug in for npm install mysql
3、 see package-lock.json Whether the file already exists mysql

Start connecting to database (MySQL)

1、 adopt require introduce mysql Plug in for ,

	let mysql = require("mysql");

2、 Transfer mysql Under the createConnection() Method , This method has 4 Parameters need to be filled ;

host : The address of the connection ; such as ：127.0.0.1 perhaps localhost
user : The user name of the connection ; such as ：root
password： Connection password ; such as ：root
database： Connected database ; such as ：student

	let connection = mysql.createConnection({
    
	    host: "127.0.0.1",
	    user: "root",
	    password: "root",
	    database: "student"
	});

3、 adopt connent() Method to determine whether the data connection is successful ！

	connection.connect((err) => {
    
	    if (err) {
    
	        console.log(' The connection fails ' + err.stack);
	        return;
	    }
	    console.log(" Successful connection ");
	})

4、 Executive execution sql sentence , Yes Two ways Optional , But they are all called query() Method to execute :
Mode one ：
Write in this method sql sentence ; Take the following query as an example ;

	connection.query("select * from student", (err, result) => {
    
	    if (err) {
    
	        console.log(" The query fails " + err.message);
	        return;
	    }
	    console.log(' The query is successful ', result);
	});

Mode two ：
Declare a store outside sql The variable of ( If you need to submit parameters, such as executing the insert statement ); Parameters inserted values It's optional , So we can pass ? Way to occupy space ！

	let sql = "insert into student values(?,?,?)";
	
	let params = ["3", " Wang Wu ", "14"];
	
	connection.query(sql, params, (err, result) => {
    
	    if (err) {
    
	        console.log(" Insert the failure " + err.message);
	        return;
	    }
	    console.log(' Insert the success ');
	})

5、 Close the connection

	connection.end();

The overall code ：

	let mysql = require("mysql");
	
	let connection = mysql.createConnection({
    
	    host: "127.0.0.1",
	    user: "root",
	    password: "root",
	    database: "student"
	});
	
	connection.connect((err) => {
    
	    if (err) {
    
	        console.log(' The connection fails ' + err.stack);
	        return;
	    }
	    console.log(" Successful connection ");
	})
	
	connection.query("select * from student", (err, result) => {
    
	    if (err) {
    
	        console.log(" The query fails " + err.message);
	        return;
	    }
	    console.log(' The query is successful ', result);
	});
	
	 let sql = "insert into student values(?,?,?)";
	
	 let params = ["3", " Wang Wu ", "14"];
	
	 connection.query(sql, params, (err, result) => {
    /
	     if (err) {
    
	         console.log(" Insert the failure " + err.message);
	         return;
	     }
	     console.log(' Insert the success ');
	 })
	
	//  Close the connection 
	connection.end();