Creating SQL Report Using QC Database

I am creating a 6 month report that shows the: Number of users who have used QC in the last six months, the log in times and log out times. It shows the users full name and what area of work they are in.

When I access the server and database, it gives me a choose a table of ALL the users in our system and their session history.

I creat two spread sheets for the two tables (Users and Session history) What we've been doing is highlighting the end time column in the session history table and creating a pivot table sorting it by user and end time.

The issue is that not all of our user show up in the pivot table, though they are there in the user table. We have 410 users in the user table but only 193 users in the session history tab.

Why is that? Is there anything different we can do? Is that how it is?

Any help would be appreciated. Let me know if more information is needed to help answer the answer.

Thank you,