title: Create a column in a table that matches a specific pattern
body: <p>Hi I am quite a beginner in pl/sql and I try to create a table with a column that should match a pattern consisting of five character string with the two first characters are letter and the other three are numbers with no <code>NULL</code> and don't start with zero.
  I have tried the alter table modify option but I get an error that what I am trying to do is not an <code>ALTER TABLE</code> option</p>
  
  <pre><code>CREATE TABLE my_course
  (my_course_firstyear VARCHAR2(2),
  my_course_secondyear NUMBER(10) NOT NULL,
  my_course_final VARCHAR2(10)); 
  
  ALTER TABLE my_course
  modify
  my_course_final VARCHAR2(20),
  my_course_secondyear || mycoursefinal);
  </code></pre>
  
  <p>Of course this is not working but I just can't work out how to set constraints when a column is a combination of letters and numbers.</p>
  
  <p>I'd appreciate your help on this.</p>