title: using an inner or left join in an update?
body: <p>Though my sql knowledge is pretty good, I cannot get my head around the difference in a <code>left</code> vs <code>inner</code> <code>join</code> specifically when doing an <code>update</code>.</p>
  
  <pre><code>employee_table
  column1:id
  column2:socialsecurity
  
  
  private_info_table
  column1:id
  column2:socialsecurity
  </code></pre>
  
  <p>I need to update <code>employee_table.socialsecurity</code> to be <code>private_info_table.socialsecurity</code></p>
  
  <p><strong>should I do a left or inner join: ???</strong></p>
  
  <pre><code>update e
  set e.socialsecurity=p.socialsecurity
  from employee_table e
  join private_info_table p  --should this be left or inner join?
  on p.id=e.id
  </code></pre>