title: When to use a left outer join?
body: <p>I don't understand the concept of a left outer join, a right outer join, or indeed why we need to use a join at all! The question I am struggling with and the table I am working from is here: <a href="http://www.cs.ucc.ie/pipermail/cs2501.2011/attachments/20110323/4288bee0/attachment-0001.pdf" rel="noreferrer">Link</a></p>
  
  <p><strong>Question 3(b)</strong> </p>
  
  <p>Construct a command in SQL to solve the following query, explaining why it had to employ the
  (outer) join method. [5 Marks]
  “Find the name of each staff member and his/her dependent spouse, if any”</p>
  
  <p><strong>Question 3(c) -</strong> </p>
  
  <p>Construct a command in SQL to solve the following query, using (i) the join method, and (ii) the
  subquery method. [10 Marks]
  “Find the identity name of each staff member who has worked more than 20 hours on the
  Computerization Project”</p>
  
  <p>Can anyone please explain this to me simply?</p>