title: SQL: select all unique values in table A which are not in table B
body: <p>I have table A</p>
  
  <pre><code>Id  | Name      | Department
  -----------------------------
  0   | Alice     | 1
  0   | Alice     | 2
  1   | Bob       | 1
  </code></pre>
  
  <p>and table B</p>
  
  <pre><code>Id  | Name
  -------------
  0   | Alice     
  </code></pre>
  
  <p>I want to select all unique Ids in table A which do not exist in table B. how can I do this?</p>