One way to join two tables is to use a nested loop. The principle is simple. Here is some pseudo code:

for x in table1: 
   for y in table2: 
         if x.field == y.field 
               issue row 
         else 
               keep doing 

Nested loops are often used if one of the sides is very small and contains only a limited set of data. In our example, a nested loop would lead to 100 million x 200 million iterations through the code. This is clearly not an option because the runtime would simply explode.

A nested loop is generally O(n2), so it is only efficient if one side of the join is very small. In this example, this is not the case, so a nested loop can be ruled out to calculate the view.