SQL: I need to find the person with the highest sales of something from a table?

SELECT SalesPerson, COUNT(Sold_by) total FROM Rents

JOIN Sales GROUP BY (SalesPerson, total) ORDER BY sold_By DESC LIMIT 1;

That's just the number of sales. If you need the total dollar amount, you should do a separate query after the first one...

SELECT SalesPerson, (Total_Price * COUNT(sold_by)) direct_sales FROM Rents

JOIN Sales GROUP BY (SalesPerson, direct_sales) ORDER BY sold_by DESC LIMIT 1;

Untested, but that should point you in the right direction. Some database systems require an AS for aliases. The aliases here are "total" in the first and "direct_sales" in the second. I'm not sure some databases can handle the second query example.

This sounds like a classic case for using a UNION; you probably want to union your Sales and Rents in a subquery, then use SUM to find the total sales for each Emp_ID.

You can probably find the biggest one by using ORDER BY and LIMIT 1.