For this use case, a relational database would be a good choice as it can easily store and retrieve structured data. Here is a possible database schema:

Table: Group

    id (primary key)
    created_at
    ended_at

Table: Microcontroller

    id (primary key)
    group_id (foreign key to Group)
    joined_at

In this schema, each group is represented as a row in the Group table with a unique ID, the time it was created, and the time it ended (if applicable). When a microcontroller joins a group, a row is added to the Microcontroller table with its own unique ID and a foreign key reference to the group it joined. The joined_at column records the time when the microcontroller joined the group.

To query the number of microcontrollers that joined a particular group and when they joined, you can use a JOIN statement between the Group and Microcontroller tables. For example:


SELECT Microcontroller.id, Microcontroller.joined_at
FROM Group
JOIN Microcontroller ON Group.id = Microcontroller.group_id
WHERE Group.id = [group ID];

This will return a list of microcontroller IDs and their join times for the specified group ID.
spam fails_task lang_mismatch pii not_appropriate hate_speech sexual_content quality toxicity humor helpfulness creativity violence