title: How to ignore the field that common in two tables
body: <p>I have two tables</p>
  
  <pre><code>t1                           t2
  -------------------         ---------------------
  no       course              no        equivalent 
  -------------------         ---------------------
  1        MATH 101             2         CHEM 111      
  2        CHEM 101
  3        ENG 101
  </code></pre>
  
  <p>How I can write query or query with function in php language that show me courses and disappear the courses that its no common between the two tables.</p>
  
  <p>likes this </p>
  
  <p>output</p>
  
  <pre><code>--------------------
  no        course
  --------------------
  1        MATH 101
  3        ENG 101
  </code></pre>
  
  <p>in the output table course number 2 <code>(  2        CHEM 101)</code> do not appear in the table because its number shared between t1 and t2 .
  I want like that.</p>