Node.js - MySQL AVG()

In this article, we would like to show you how to use SQL AVG() function in Node.js.

Note: at the end of this article you can find database preparation SQL queries.

Example 1

const mysql = require('mysql');

const connection = mysql.createConnection({        // gets connection with database
    host: 'localhost', // '127.0.0.1'
    user: 'root',
    password: 'password',
    database: 'my_database',
});

connection.connect(error => {
    if (error) throw error;
    const query ='SELECT AVG(`salary`) FROM `users`';

    connection.query(query, (error, result) => {   // sends queries
        connection.end();                          // closes connection
        if (error) throw error;
        console.log(result);
    });
});

Output: 

[ { 'AVG(`salary`)': 3631.25 } ]

Example 2

const mysql = require('mysql');

const connection = mysql.createConnection({        // gets connection with database
    host: 'localhost', // '127.0.0.1'
    user: 'root',
    password: 'password',
    database: 'my_database',
});

connection.connect((error) => {
    if (error) throw error;
    const query ='SELECT * FROM `users`' +
                 'WHERE `salary` < (SELECT AVG(`salary`) FROM `users`)';

    connection.query(query, (error, result) => {   // sends queries
        connection.end();                          // closes connection
        if (error) throw error;
        console.log(result);
    });
});

Output:

Database preparation

create_tables.sql file:

CREATE TABLE `users` (
	`id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
	`name` VARCHAR(50) NOT NULL,
	`surname` VARCHAR(50) NOT NULL,
	`department_id` INT(10) UNSIGNED,
    `salary` DECIMAL(15,2) NOT NULL,
	PRIMARY KEY (`id`)
);

insert_data.sql file:

INSERT INTO `users`
	( `name`, `surname`, `department_id`, `salary`)
VALUES
	('John', 'Stewart', 1, '3512.00'),
	('Chris', 'Brown', 2, '1344.00'),
	('Kate', 'Lewis', 3, '6574.00'),
	('Ailisa', 'Gomez', NULL, '6500.00'),
	('Gwendolyn', 'James', 2, '4200.00'),
	('Simon', 'Collins', 4, '3320.00'),
	('Taylor', 'Martin', 2, '1500.00'),
	('Andrew', 'Thompson', NULL, '2100.00');