title: Database (MySQL) structuring: pros and cons of multiple tables
body: <p>I am collecting  data and storing it MySQL, for:</p>
  
  <ul>
  <li>75 variables</li>
  <li>55 countries</li>
  <li>Each year</li>
  </ul>
  
  <p>I have, at this stage since I am building this tool created a single table, of variables / countries (storing 1 year worth of data).</p>
  
  <p>Next year (and for several years after that) a new set of data will be input for each country.</p>
  
  <p>There are therefore 3 variables in controlling data returned to a user reviewing all collected data. The general form of any query would be:</p>
  
  <ul>
  <li>Show me <strong>these</strong> specifics variables, for <strong>these</strong> specific countries, for <strong>these</strong> specific years.</li>
  </ul>
  
  <p>(Show me average age and weight, for USA and Canada, for 2012 and 2009, for example)</p>
  
  <p>My question is, it seems that I have two options for arranging this data:
  -Multiple tables where I create a table of <em>country / variable</em> for each year data is collected
  - Single table and simply add a column (field) for the year that data relates to.</p>
  
  <p>As far as I can tell I could make these database calls with either sructure, but is one more powerful / efficient / quicker, and why?</p>
  
  <p>Thanks for your consideration.</p>
  
  <p>It's a PDO / PHP interface if that is relevent.</p>