Cascading drop-down box implementation (PHP)

Cascading drop-down boxes are a common form interaction method that can dynamically load subsequent drop-down box options based on the selection of the previous drop-down box. This interaction method is often used in scenarios where data needs to be filtered or classified based on user selection. In this article, we will use PHP to implement cascading drop-down boxes and provide the corresponding source code.

First, we need to prepare the corresponding data. Suppose we have a city-region data relationship and need to implement a cascading drop-down box to load the corresponding regional options based on the city selected by the user.

The database table structure is as follows:

CREATE TABLE cities (
    id INT PRIMARY KEY,
    name VARCHAR(50)
);

CREATE TABLE areas (
    id