How to check if an item exist in another table.

Question

for a lab I need to make a trigger that checks to see if a item exists in a different table. I cant
figure out how to check for the life of me.

Answer 1

I think you need to be more descriptive about that, what is this "item" you are looking for, is it a field? an expression of several conditions or values?.

Also, it would help if you describe the tables' structures, and your current trigger implementation (query) so people here can see clearly the problem, and offer suggestions or solution, looking forward to your feedback :)