如何使用特定字母生成ID并在PHP中添加数字?

As question.

I need to generate a few case id when I insert into database tables case id examples: PR000001

Letter distribution: -
- PR=Projector
- TV=Television
- PC=Personal Computer
Numbering: Add 1 each time I insert into database table.

But I'm confused in how to get newest case id from database table and add 1 being generate a new relative case id.


Simple to say:

Projector newest case id = PR001
Projector generated newest case id = PR002

Television newest case id = TV003
Television generated newset case id = TV004

How to realize it? I have tried for created two columns but it become more trouble...