ignore mysql duplicate data insert if no duplicate data

Hello, I'm a beginner at mysql.

c# is currently using mysql. I feel difficult and ask for advice while doing it, so I ask for advice.

The data in the DB is being updated, ignored, and if not, INSERT. There may be content 1 in category 100,101, but content 1 should not be duplicated in category 100. It is necessary because the categories 100 and 101 are always overlapped whenever INSERT is done.

Thank you.