I built a database and have about 8 different tables for different kinds of items. I did this because each table is a category and each item has different fields so I couldn't make them all 1 table. The problem I'm running into is that I need the itemID field to be unique across all tables. Not just unique to each table. 

For example, if an admin adds an item in 1 table, the itemID for that item can't be a duplicate of another item in a different table or it will cause problems for me. Please help me set this correct. Can I do this directly in the database? Or do I need to make a php script to check if the item number already exists?

I hope I explained that right. :)