Three-level non-refresh drop-down menu

A three-level non-refresh drop-down menu calls provincial and municipal data. All data is saved to the mysql database, which is directly connected to the Mysql database. Import the database and run it directly. In fact, with this example, we can do it It would be good to create other applications and draw inferences from one example, such as creating a three-level classification of news. As a reminder, if you want to integrate it into an established website, you only need to import the data table, modify the database connection code appropriately, and the calling code remains unchanged.