title: Compound key/ Composite Key / Concatenated Key / Aggregate Key / Candidate Key
body: <p>Can anyone please give me a clear idea of the difference of these keys?</p>
  
  <ol>
  <li>Compound key </li>
  <li>Composite Key </li>
  <li>Concatenated Key</li>
  <li>Aggregate Key</li>
  <li>Candidate Key</li>
  </ol>
  
  <p>I searched for the definitions of all these and it seems some of them are just synonyms. But not sure if I understood then correctly. I would be thankful if someone can come up with a descriptive answer comparing the differences and similarities.</p>