Avoid a Cartesian plan in a Join with 2 tables with duplicities

Question

According to the image above:

The field A1 of TableA has two duplicate values which is key 3 and the TableB with the countryside B1 has the same duplicate values.

I wanted to make a inner join between the two tables using the fields A1 of TableA and B1 of TableB as keys and bring as results the field values A2 and B2 without generating a Cartesian.

Intended result:

A2 B2 
a   a
b   a    
c   c 
d   f 

I tried to make:

Select  A2, b.B2 
    from Table_A as a 
    inner join Table_B  as b
    on a.a1 = b.b1  

Result acquired with the query above:

A2, B2
a   a
b   a
c   c
d   c
c   f
d   f