Question 1.a. looks like it might require a Full Outer Join between the Users table and the Informations table (what a horrible name that is for a table) based on the respective timestamp columns. It doesn't say whether or not the timestamps have a time in them so I would assume they do and you should convert them to just the day to compare them.
Question 1.b. looks like it'll use the same two tables but with an Outer Join only to the Informations table.
Knowing that, give it a try. I don't know in the write-up what they mean when they say "Tasks 1b and 3b also require further written explanations". I'm thinking that they want you to explain how the queries you write actually work and why you made it work that way.
Now, just so you know, there are a whole lot of reasons why we're all hesitant to help you with actual code...
- If this IS for an interview, we don't want to help you get the job because the company would suffer from your lack of knowledge.
- If we've misunderstood the question and give you the wrong answer, we don't want to be blamed for trying to help and getting it wrong.
- You NEED to TRY first! You done nothing to show us any motivation on your part. So, give it a try. I even gave you some hints as to what to look for.
- All the reasons also apply to homework.