title: What do $1 and $2 mean?
body: <p>What do the $1 and $2 in this line of code mean? Are they variables? But then how can they be used in a string?</p>
  
  <pre><code>$query = "select * from php_project.student where student_num=$1 and student_pass=$2";
  </code></pre>
  
  <p>EDIT: here are the next few lines:</p>
  
  <pre><code>        $stmt = pg_prepare($dbconn,"ps",$query);
          $result = pg_execute($dbconn,"ps",array($studentnum,$password));
          if (!$result){
              die("error in SQL query:".pg_last_error());
          }
  </code></pre>