I'm taking a guess as to what kind of structure you want. You have tables of Lectures and Trainings, and you've linked them, but now you want a list of all unique Lecture + Training combinations, correct?

I would recommend that you instead link Lectures and Trainings in the Lecture + Training table, instead of to each other. That way the Lecture + Training table is essentially "free".

As an aside, there are some tweaks you can make to your existing tables to make them more user-friendly:

• Airtable doesn't need an ID field, so you can instead set your Name field as the primary field, even if you have duplicate values (if you'd like, you can use a formula to combine Name and Date for disambiguation).
• Airtable allows spaces in field names, so instead of "training_id", you could have "Training ID".
• If you convert {training_id} and {lecture_id} to "Link to another field" fields, Airtable will convert the existing values to links.