title: subquery runs for each record?
body: <p>my doubt is if i write subquery in where clause , then this subquery will execute for each record or only once.
  for example,</p>
  <pre><code>select *
  from emp
  where empno in (select empno from emp);
  </code></pre>
  <p>and if i have query like this then what will happen?</p>
  <pre><code>SELECT *
  FROM emp
  WHERE EXISTS (SELECT 'RANDOM' FROM dual)
  </code></pre>