I made a mess of my description. :'-( Instead of topic and subtopcs I should have use Main Topic and Non Main Topics. I have tasks. Every task has a Main Topic and optionally Non Main Topics. For example a task can be primarily connected to work, but also be related to Familie and Hobbies. So the link table contains the above records, but cannot contain: 17 1 because 1 is already filled in the Main Topic. A record with id 18 can have a topicID of 4 and the link table contains: 18 1 because the Main Topic is Hobbies and there is also a Non Main Topic Work. But it cannot contain: 18 4, because 4 is the Main Topic and cannot be a Non Main Topic. I hope I am clear enough now, but do not hesitate to ask.