title: Equivalent Relational Algebra statement for a given SQL query
body: <p>The following SQL:</p>
  
  <pre><code>SELECT DISTINCT a1,a2,a3.....an
  FROM   R1,R2,R3......Rm
  Where P
  (P is any predicate)
  </code></pre>
  
  <p>I want to know what could possibly be its equivalent Relational Algebra. I think it might be something like this:
  <code>πa1,a2,a3...an(σP(R1 U R2 U R3 ....U Rm)</code>.
  But again I am not sure whether I am correct. Can anyone help me with its correct equivalent in Relational Algebra?</p>