Combine totals from three tables in one report?

Combine totals from three tables in one report?

I'm not very familiar with Zoho Reports, or relational databases, so I'm hoping someone can help.  I have three different tables that contain sales data from three different kinds of products - our main product, services, and accessories.  I'm wanting to combine the total profits from each of these tables to create a report of total profits.  I've seen that you can connect different tables with lookup columns, but these tables don't have any common columns except the date the transaction took place, and the profit of the transactions.  I don't think I'd use lookup columns to connect them.  I just want to total the profits of the three tables together in the same report.  How would I do that?