How to use mysql in nodejs

Node.js is a very popular server-side JavaScript runtime environment that can be used to build high-performance web applications and APIs. Compared with other server-side programming languages, Node.js provides a powerful and flexible development platform that can easily integrate various third-party libraries and modules, including the MySQL database. In this article, we will explore how to connect and operate a MySQL database using Node.js.

MySQL is a popular relational database management system. In Node.js, various modules can be used to connect and operate MySQL database. Here, we will use Node.js’s mysql module to achieve this.

Before you begin, make sure you have installed Node.js and a MySQL database, and that you have created a database and a table. In this article, we will use a database named "test" and a table named "users". This table has three fields: id (incremented), name and email. The following is the SQL command to create the table:

CREATE TABLE users (
id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(30) NOT NULL,
email VARCHAR(50) NOT NULL
);

Install the mysql module

Before using the mysql module, you first need to install it. You can install the mysql module using npm (Node.js package manager). Open a terminal window and run the following command:

npm install mysql

Connect to a MySQL database

Here is the basic code on how to connect to a MySQL database:

const mysql = require('mysql');

const connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: 'root ',
database: 'test'
});

connection.connect((err) => {
if (err) throw err;
console.log( 'Connected!');
});

In this example, we first import the mysql module, and then use the mysql.createConnection() function to create a connection object. To do this, we need to pass in some connection parameters, including hostname, username, password, and database name.

After creating a connection object, we can use the connection.connect() method to connect to the MySQL database. If the connection is successful, it will output a "Connected!" message. If the connection fails, an error will be thrown.

Query MySQL database

After connecting to the MySQL database, we can perform various queries and operations. Here is the basic code of how to query the data in the table:

const mysql = require('mysql');

const connection = mysql.createConnection({
host: 'localhost' ,
user: 'root',
password: 'root',
database: 'test'
});

connection.connect((err) => {
if (err) throw err;
console.log('Connected!');

connection.query('SELECT * FROM users', (error, results, fields) => {

if (error) throw error;
console.log(results);

});
});

In this example, we use the connection.query() method to execute a SQL query statement. In this example, we query all the data in the users table and print the results to the console. The query results will be returned in the form of an array. Each row is an object containing the value of each field. For example, for our example, each object will have id, name and email properties.

Insert data into MySQL database

The following is the basic code on how to insert data into the table:

const mysql = require('mysql');

const connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: 'root',
database: 'test'
}) ;

connection.connect((err) => {
if (err) throw err;
console.log('Connected!');

const sql = "INSERT INTO users (name, email) VALUES ('John Doe', 'johndoe@gmail.com')";
connection.query(sql, (error, result) => {

if (error) throw error;
console.log("1 record inserted");

});
});

In this example, we use the SQL INSERT statement to insert a new record into the users table. In the connection.query() method, we pass it the SQL statement as the first parameter, and then we use a callback function to handle the response.

Update MySQL database

The following is the basic code of how to update the data in the table:

const mysql = require('mysql');

const connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: 'root',
database: 'test'
});

connection.connect((err) => {
if (err) throw err;
console.log('Connected!');

const sql = "UPDATE users SET email='john.doe@gmail.com' WHERE name='John Doe'";
connection.query(sql, (error, result) => {

if (error) throw error;
console.log(result.affectedRows + " record(s) updated");

});
});

In this example, we use the SQL UPDATE statement to update the data in the users table. We use the WHERE clause to specify the rows to be updated. In the callback function of the connection.query() method, we output the number of affected rows.

Delete data in MySQL database

The following is the basic code on how to delete data from the table:

const mysql = require('mysql');

const connection = mysql.createConnection({
host: 'localhost',
user: 'root',
password: 'root',
database: 'test'
}) ;

connection.connect((err) => {
if (err) throw err;
console.log('Connected!');

const sql = "DELETE FROM users WHERE name='John Doe'";
connection.query(sql, (error, result) => {

if (error) throw error;
console.log(result.affectedRows + " record(s) deleted");

});
});

在这个例子中，我们使用SQL DELETE语句从users表中删除数据。我们使用WHERE子句来指定要删除的行。在connection.query()方法的回调函数中，我们输出受影响的行数。

总结

在本文中，我们介绍了如何使用Node.js连接和操作MySQL数据库。我们使用Node.js的mysql模块来连接到数据库，执行各种查询和操作。使用这些知识，您可以创建强大和高效的Web应用程序和API，以及进行其他有关MySQL数据库的编程任务。

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