the table that
the <em>combination</em> of <code>from_id</code> and <code>to_id</code> must be unique 
in this table (i.e. we cannot insert duplicate rows) in our database.
</font><pre><font size="4" color="blue">
CREATE TABLE Follows 
    (from_id INTEGER, to_id INTEGER, UNIQUE(from_id, to_id) )
</font></pre><font color="black">When we add <tt>UNIQUE</tt> clauses to our tables, we are communicating a set
of rules that we are asking the database to enforce when we attempt to insert
records. We are creating 