title: Mysql function call
body: <p>If I call a function several time then will it execute every time or just execute once and the value will be used then after several time?
  Example:</p>
  
  <pre><code> select my_function('filed'),my_function('filed')/field2, 
          (my_function('filed')*field1)/field3,
  ...... from my_table    where group by filed1;
  </code></pre>
  
  <p>My question is  <code>my_function('filed')</code> will be executed once and then the result will be used in <code>my_function('filed')/field2</code> and <code>(my_function('filed')*field1)/field3</code> or every time <code>my_function('filed')</code> will be called and executed in system level ?</p>