Node.js MySQL Select Unique

In Node.js, you may want to retrieve a list of unique values from a MySQL table. In this tutorial, we'll discuss how to use the DISTINCT keyword in a SELECT statement to retrieve only unique values from a MySQL table using the node-mysql package.

Syntax

The syntax for retrieving unique values from a MySQL table is as follows:

SELECT DISTINCT column_name FROM table_name;

The DISTINCT keyword is used before the column name to specify that only unique values should be retrieved.

Example

Let's say we have a MySQL table called "customers" that contains the columns "id", "name", and "email". Here's how we can retrieve a list of unique email addresses from the table using the node-mysql package:

const mysql = require('mysql');

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

connection.connect();

connection.query('SELECT DISTINCT email FROM customers', function (error, results, fields) {
  if (error) throw error;
  console.log(results);
});

connection.end();

When we run the code above, we should see a list of unique email addresses printed to the console.

Output

The output of the example above will be a list of unique email addresses retrieved from the "customers" table in the "mydb" database.

Explanation

In the example above, we used the node-mysql package to connect to a MySQL database and retrieve a list of unique email addresses from the "customers" table using a SELECT statement. We used the DISTINCT keyword before the "email" column name to specify that we only wanted to retrieve unique email addresses. Finally, we printed the results to the console.

Use

Retrieving unique values from a MySQL table can be useful for a variety of purposes, such as generating lists of distinct items or calculating the number of unique values in a dataset.

Important Points

• Be aware that using the DISTINCT keyword can slow down the performance of your query, particularly if you are retrieving unique values from a large table.
• Always sanitize user inputs to prevent SQL injection attacks.
• Be aware of character encoding issues when working with non-ASCII data.

Summary

In this tutorial, we discussed how to retrieve unique values from a MySQL table using the node-mysql package in Node.js. We covered the syntax, example, output, explanation, use, important points, and summary of selecting unique values from a MySQL table in Node.js. With this knowledge, you can now retrieve only unique values from a MySQL table using Node.js and the node-mysql package.