title: cassandra: variable number of column in single row
body: <p>i want to design column family to store chatting history for couple of clients ,
   storing all the history for one particular couple in one row,
   for a given row,how  we store only the columns required for that row. </p>
  
  <p>Sample:</p>
  
  <pre><code>id1 | id2 | message1 | message2
  5     2     "hey"      "why"
  id1| id2  | message1 | message2 | message3 | message4
  2     3     "dcx"       "ddfs"    "ddd"         "dd"
  
  id1| id2  | message1 | message2 | message3 | message4
  4     6     "dcx"       "ppp"    
  
  create columnfamily chat (id1 int,id2 int primary key)
  insert into chat(id1,id2) values(8103333,8104444);
  </code></pre>
  
  <p>i want to add new columns <code>'message1'</code>,<code>'message2'</code> ......etc in the same row 
  so how i can create columns in a particular row 
  iam useing cqlsh 2.3.0 | cassandra 1.2.1 | cql space 3.0.0</p>