title: How Join works in SQL?
body: <p>If I have three tables say A,B and C</p>
  
  <p>A is join to B and
  B is join to C</p>
  
  <p>Then is it required to join A to C?</p>
  
  <p>I tried this with join A to C and because of this my query performance is increased but I dont understand how my query performance increased?</p>
  
  <p>It will be very helpful if you can explain me why A to C join increase the performance?</p>
  
  <p>there are 3 tables. 
  <code>AWARD_MEMBER</code>, <code>HOUSEHOLD_MEMBER</code> and <code>CONDITIONALITY_GROUP</code> 
  This is how i joined them,</p>
  
  <pre><code>AWARD_MEMBER.HH_MEMBER_ID = HOUSEHOLD_MEMBER.HH_MEMBER_ID AND 
  HOUSEHOLD_MEMBER.HH_MEMBER_ID = CONDITIONALITY_GROUP.HH_MEMBER_ID AND
  AWARD_MEMBER.HH_MEMBER_ID = CONDITIONALITY_GROUP.HH_MEMBER_ID
  </code></pre>
  
  <p>say <code>AWARD_MEMBER as A,</code> <code>HOUSEHOLD_MEMBER as B</code> and <code>CONDITIONALITY_GROUP as C</code>
  so <code>AWARD_MEMBER.HH_MEMBER_ID = CONDITIONALITY_GROUP.HH_MEMBER_ID</code> join is really required in query? If yes then how it works?</p>
  
  <p>Thanks,
  Sandeep </p>