If I have to predefine all the columns, how do I take the advantage of the variable column key/value structure of cassandra? If I use update table command, it will insert null for all the rows which don't have that column. This is same as relational DB.

For example, for contact column family, I have name, phone, email. I have 100 contacts have all 3 field. Then number 101 contact has skype id which I want to add. If I use insert statement, it won't let me add skypeid since it's not defined in the CF. So I have to run alter statement to change the CF, then all the first 100 contacts will have a null field for each of them.