title: SQL - Check table for new rows?
body: <p>I have two tables, for example:</p>
  
  <pre><code>Table A                                  Table B
  =======                                  =======
  
  Name         | Color                     Name         | Color
  ----------------------                   ----------------------
  Mickey Mouse | red                       Mickey Mouse | red
  Donald Duck  | green                     Donald Duck  | blue
  Donald Duck  | blue                      Minnie       | red
  Goofy        | black
  Minnie       | red
  </code></pre>
  
  <p>Table A is my source table and B is the destination table. Now I need a query which finds all the different (additional) rows in table A so table B can be updated with those rows.
  So I need a query which finds me the following rows from table A:</p>
  
  <pre><code>Name         | Color  
  ----------------------
  Donald Duck  | green  
  Goofy        | black
  </code></pre>
  
  <p>What is a good approach for such a query? It should be as efficient as possible (avoid too many joins).
  Thanks for any help!</p>