title: Invalid Subquery yet outer query returns the records
body: <p>I've two table EMP &amp; DEPT. Below are the descriptions.</p>
  
  <pre><code>**EMP table:**
  
  EMP_ID        NUMBER      
  EMP_NAME      VARCHAR2(4)
  
  **DEPT table:**
  
  DEPT_ID        NUMBER      
  DEPT_NAME      VARCHAR2(4)
  </code></pre>
  
  <p>when i run the below query it executed successfully even though the subquery is invalid.</p>
  
  <pre><code>SELECT * FROM EMP WHERE EMP_ID IN (SELECT SAL FROM DEPT);
  </code></pre>
  
  <p>I am expecting <strong>ORA-00904 : invalid identifier</strong>, but it returns the records from EMP table.</p>