unexpected result from equality check (mysql)

Question

The objective of the assignment is as follows: List the products where the reorder level is equal to the units in stock. Display the supplier id and supplier name from the Suppliers table, the product name, reorder level, and units in stock from the Products table. Order the result set by the supplier id. The query should produce the result set listed below.

However my code affects way more than 4 rows:

select Suppliers.SupplierID,Suppliers.Name,Products.ProductName,Products.ReorderLevel,
Products.UnitsInStock
from Suppliers,Products 
where Products.ReorderLevel = Products.UnitsInStock
group by Suppliers.SupplierID,Suppliers.Name,Products.ProductName,Products.ReorderLevel,Products.UnitsInStock