Updating Data in MySQL Database from Node.js

Summary: in this tutorial, you will learn how to update data in the MySQL database from a Node.js application.

This tutorial picks up where the Querying Data in MySQL Database from Node.js tutorial left off.

Updating data

To update data in a table in MySQL from a Node.js application, you follow these steps:

• Connect to the MySQL database server.
• Execute an UPDATE statement by calling the query() method on a Connection object.
• Close the database connection.

The following update.js program sets the value of the completed column of row id 1 in the todos table to false:

let mysql = require('mysql');

let connection = mysql.createConnection({
  host: process.env.DB_HOST,
  port: process.env.DB_PORT,
  user: process.env.DB_USER,
  password: process.env.DB_PASSWORD,
  database: process.env.DB_NAME,
});

connection.connect((err) => {
  if (err) return console.error(err.message);

  let sql = `UPDATE todos
           SET completed = ?
           WHERE id = ?`;

  let data = [false, 1];

  connection.query(sql, data, (error, results, fields) => {
    if (error) return console.error(error.message);
    console.log('Rows affected:', results.affectedRows);
  });

  // close the database connection
  connection.end();
});Code language: JavaScript (javascript)

How it works.

First, import the mysql module:

let mysql = require('mysql');Code language: JavaScript (javascript)

Second, create a connection to the MySQL database using the createConnection method:

let connection = mysql.createConnection({
  host: process.env.DB_HOST,
  port: process.env.DB_PORT,
  user: process.env.DB_USER,
  password: process.env.DB_PASSWORD,
  database: process.env.DB_NAME,
});Code language: JavaScript (javascript)

Note that we retrieve the connection parameters (host, port, user, password, and database) from environment variables using .env.

Third, connect to the MySQL database:

connection.connect((err) => {
  if (err) return console.error(err.message);
});Code language: JavaScript (javascript)

This code checks and logs for any connection errors if any.

Fourth, define an SQL query to update a record in the todos table:

let sql = `UPDATE todos
           SET completed = ?
           WHERE id = ?`;Code language: JavaScript (javascript)

Fifth, specify the data used in the query:

let data = [false, 1];Code language: JavaScript (javascript)

In this case, the first placeholder ? in the SQL query will be replaced by false, and the second placeholder ? will be replaced by 1.

Sixth, execute the SQL query using the query method:

connection.query(sql, data, (error, results, fields) => {
  if (error) return console.error(error.message);
  console.log('Rows affected:', results.affectedRows);
});Code language: JavaScript (javascript)

This code executes the query and displays the number of rows affected.

Finally, close the database connection:

connection.end();
Code language: CSS (css)

Verify the update

First, retrieve the row with id 1 from the todos table:

SELECT * FROM todos WHERE id = 1;

Output:

+----+-------------------------------+-----------+
| id | title                         | completed |
+----+-------------------------------+-----------+
|  1 | Learn how to insert a new row |         1 |
+----+-------------------------------+-----------+
1 row in set (0.00 sec)Code language: JavaScript (javascript)

Second, run the update.js program.

node --env-file .env update.jsCode language: CSS (css)

The output indicates that the number of updated rows is 1.

Third, query data from the todos table:

select * from todos where id=1;Code language: JavaScript (javascript)

Output:

+----+-------------------------------+-----------+
| id | title                         | completed |
+----+-------------------------------+-----------+
|  1 | Learn how to insert a new row |         0 |
+----+-------------------------------+-----------+
1 row in set (0.00 sec)Code language: JavaScript (javascript)

The data showed that the value in the completed column was updated to 0.

In this tutorial, you have learned how to update data in a MySQL table from a Node.js application.