What query language is most common for e-journal searches? I need to teach a quick lesson on e-journal searching, e.g. to search for one item, excluding certain terms, or another item.

What is the most common query language that students will most likely encounter?
Academic databases are built for people who have no idea what a 'query language' is. I agree that the world would be a much better place if everyone knew a little bit of SQL, but it's not like that.

The only exception that I know is Zentralblatt, an academic database specialized to mathematics which includes a sort of text-based query language.

Every other academic database that I have worked with uses custom-made input masks where you can select manually fields to search on and logical operators; they look like this example, again from Zentralblatt.