title: How to properly create composite primary keys - MYSQL
body: <p>Here is a gross oversimplification of an intense setup I am working with. <code>table_1</code> and <code>table_2</code> both have auto-increment surrogate primary keys as the ID. <code>info</code> is a table that contains information about both <code>table_1</code> and <code>table_2</code>.</p>
  
  <pre><code>table_1 (id, field)  
  table_2 (id, field, field)
  info ( ???, field)
  </code></pre>
  
  <p>I am trying to decided if I should make the primary key of <code>info</code> a composite of the IDs from <code>table_1</code> and <code>table_2</code>. If I were to do this, which of these makes most sense?<br>
  <em>( in this example I am combining ID 11209 with ID 437 )</em> </p>
  
  <p><code>INT(9)</code> 11209437   <em>(i can imagine why this is bad)</em><br>
  <code>VARCHAR (10)</code>    11209-437<br>
  <code>DECIMAL (10,4)</code> 11209.437   </p>
  
  <p>Or something else? </p>
  
  <p>Would this be fine to use this as the Primary Key on a MYSQL MYISAM DB?</p>