Introduction

When you enter a website URL in your browser, you may notice that some websites have a prefix in front of their domain name, such as "blog.example.com" or "store.example.com". This prefix is known as a subdomain.

A subdomain is a way to divide a website into smaller sections or departments. It allows you to organize your website content and provide a more personalized experience for your users. For example, a company may use a subdomain to host their blog content or to sell products in an online store.

But how can you use subdomains to query a database and retrieve specific information based on the subdomain?

One way to accomplish this is by using the subdomain as a parameter in your database queries. For example, let's say you have a website that uses subdomains to differentiate between different product categories. You can create a database table for each subdomain and use the subdomain as a parameter to query the appropriate table.

Here's an example of how this could work:

• You have a website that sells products in different categories, such as "electronics", "clothing", and "home goods".

• Each category has its subdomain, such as "electronics.example.com", "clothing.example.com", and "homegoods.example.com".

• You create a separate database table for each category, such as "electronics_products", "clothing_products", and "homegoods_products".

• When a user visits one of the subdomains, such as "electronics.example.com", you can extract the subdomain from the URL using Express middleware and use it as a parameter in your database query, like this:

app.use(function(req, res, next) {
  req.subdomain = req.hostname.split('.').shift();
  next();
});
// or 
app.get('/', function(req, res) {
// use req.subdomains which is default.
  var subdomain = req.subdomain;
  var sql = 'SELECT * FROM ' + subdomain + 'products';
  // execute the SQL query and return the results
// if error handle it using catch and return 'user not found'
});

In this example, the Express middleware extracts the subdomain from the hostname and sets it as a property of the req object. The app.get() route then retrieves the subdomain from the req object and uses it to construct the SQL query.

This approach allows you to keep your database tables organized and retrieve data based on the subdomain, providing a more personalized experience for your users.

In conclusion, subdomains can be a powerful tool for organizing your website content and providing a personalized experience for your users. By using subdomains as a parameter in your database queries, you can retrieve specific information based on the subdomain and create a more tailored experience for your users.