title: Joins / Sub queries dilemma
body: <p>I come across several instances where I can write a query with using both joins or sub queries. I usually use joins but sometimes use sub queries (without any reason). I have read in several places (including stackoverflow) that joins are faster than sub queries in many instances but sometimes subqueries are faster. Right now the queries I am writing does not deal with large amount of data so I guess the speed isn't much of a concern. But for future, I'm curious about the following.</p>
  
  <p>a.) Why are joins faster than subqueries (in general).</p>
  
  <p>b.) What are the instances when subqueries are faster. How will I know?</p>
  
  <p>c.) If I'm writing a query, how should I judge whether I should use subquery or a join. I will appreciate if someone explains me with an example. </p>