Hi Armin,
You just need two nodes: 
Node 1 is your input data-set with the two columns, Node 2 is a simple join where you select Column A and Column B as the respective joining columns.
For Example1: this will list the value that exist in both data-sets in the first column of the Joiner output.
For Example2: this will create an empty table since there are no matching values.
Cheers,
Medzi