How to achieve three-level linkage

Question

I now need a registration system. There are two tables now, the unit table and the position table. The position code in the position table is unique. The function I need to implement is that when the unit is selected, the unit will be automatically filtered out. All the position codes corresponding to the unit, and then filter out the professional names based on the position codes

Can anyone help me

Answer 1

1. Every time you select, request the backend interface (ajax call) to obtain the next level data.

2. The backend passes three interrelated arrays to the frontend. Each selection does not request the backend interface, and the frontend completes the filtering itself.

Answer 2

www.php.cn has such a video tutorial

Answer 3

Baidu