Welcome to the forum. These are two separate questions:
This part is pretty simple. Just write a query that returns two columns: a timestamp and a user count.
Then configure a line chart visualization like this:
This one is more complicated. Redash gets the latest data from your DB when you run a query; and it doesn’t remember old results after that. So to do this, your database will do the heavy lifting. Redash is just there to visualize what your DB kicks out.
Here are two approaches I’ve used in the past:
- Write a stored procedure that counts your users twice each day and
INSERT's the results to a new a table. Then query that new table with Redash. The downside here is that your history begins today.
- Write a query that can calculate your count of users at an arbitrary time and then
GROUP BY a twice-daily interval. The downside here is complexity, as there is no “best approach”. It depends entirely on your database schema.