(德文) Duda sobre las llavees foráneas de la fila con un dato nulo que nunica debió serlo (法语)

Hello Brais, first of all, congratulations on your great work, I'm loving the video ❤️ My question is about a specific section of the video, specifically at 4:17:53. We are analyzing N:M relationships; and you show us the importance of declaring the attributes of the columns well with an example, in which we want to relate a user table to the programming languages they know how to program. First, you show us how the data is inserted ( INSERT INTO users_languages(users_id, languages_id) VALUES (1,1)), and then (4:22:13) you only include the first field ( INSERT INTO users_languages(users_id) VALUES (1)). Workbench screams "the following task will not be executed" because we have not specified that neither users_id nor languages_id are not null (4:23:55).

After that, you delete the row, try to update the table so that it does not accept non-null values, and then it screams because it has foreign keys. But right after that, it lets you change the table attributes (4:25:30) and I don't really understand why, what changed from one moment to the next? In the video, it seems that you don't change anything, you just review the tables. I don't know if it's visible on the Twitch live stream, but I'd like to know what to do in the hypothetical case that something similar happens to me.