I recently had to create a report that combined all three of these tables, Change Request, Change Task, & Approval. Still being relatively new to ServiceNow, the process in this article wasn't obvious to me until I read several different articles, so thank you to everyone who participates in this community, you all are life savers!

To combine all three of these tables I created a database view with the following settings:

Steve Bell did an excellent video on database views that helped me a lot in getting this created.

Ask the Expert: Creating a Database View with Steve Bell - YouTube